Object API

The object API deals with all the operations shared by objects, value types, arrays.

The object API has methods for accessing fields, properties, methods, events, delegates.

There are some advanced uses that are useful to document here dealing with remote fields.

Synopsis

#include <metadata/object.h> typedef struct MonoVTable MonoVTable; typedef struct _MonoThreadsSync MonoThreadsSync; typedef struct { MonoVTable *vtable; MonoThreadsSync *synchronisation; } MonoObject; typedef struct { guint32 length; guint32 lower_bound; } MonoArrayBounds; typedef struct { MonoObject obj; /* bounds is NULL for szarrays */ MonoArrayBounds *bounds; /* total number of elements of the array */ guint32 max_length; /* we use double to ensure proper alignment on platforms that need it */ double vector [MONO_ZERO_LEN_ARRAY]; } MonoArray;

`MonoObject` is the base definition for all managed objects in the Mono runtime, it represents the System.Object managed type.

All objects that derive from System.Object do have this base definition. Derived objects are declared following the pattern where the parent class is the first field of a structure definition, for example:

typedef struct { MonoObject parent; int my_new_field; } MyNewObject

Core Object Methods

mono_object_new
Syntax
MonoObject* mono_object_new (MonoDomain *domain, MonoClass *klass)

Parameters
klass the class of the object that we want to create
Return value
a newly created object whose definition is looked up using klass. This will not invoke any constructors, so the consumer of this routine has to invoke any constructors on its own to initialize the object.

It returns NULL on failure.

For example, if you wanted to create an object of type System.Version, you would use a piece of code like this:

MonoClass *version_class; MonoObject *result; /* Get the class from mscorlib */ version_class = mono_class_from_name (mono_get_corlib (), "System", "Version"); /* Create an object of that class */ result = mono_object_new (mono_domain_get (), version_class);
mono_object_new_alloc_specific
Syntax
MonoObject* mono_object_new_alloc_specific (MonoVTable *vtable)

Parameters
vtable virtual table for the object.
Return value
the allocated object.
Description
This function allocates a new MonoObject with the type derived from the vtable information. If the class of this object has a finalizer, then the object will be tracked for finalization.

This method might raise an exception on errors. Use the mono_object_new_fast_checked method if you want to manually raise the exception.

mono_object_new_fast
Syntax
MonoObject* mono_object_new_fast (MonoVTable *vtable)

Parameters
vtable virtual table for the object.
Return value
the allocated object.
Description

This function allocates a new MonoObject with the type derived from the vtable information. The returned object is not tracked for finalization. If your object implements a finalizer, you should use mono_object_new_alloc_specific instead.

This method might raise an exception on errors. Use the mono_object_new_fast_checked method if you want to manually raise the exception.

mono_object_new_from_token
Syntax
MonoObject* mono_object_new_from_token (MonoDomain *domain, MonoImage *image, guint32 token)

Parameters
image Context where the type_token is hosted
token a token of the type that we want to create
Return value
A newly created object whose definition is looked up using token in the image image
mono_object_new_specific
Syntax
MonoObject* mono_object_new_specific (MonoVTable *vtable)

Parameters
vtable the vtable of the object that we want to create
Return value
A newly created object with class and domain specified by vtable
mono_object_clone
Syntax
MonoObject* mono_object_clone (MonoObject *obj)

Parameters
obj the object to clone
Return value
A newly created object who is a shallow copy of obj
mono_object_get_class
Syntax
MonoClass* mono_object_get_class (MonoObject *obj)

Parameters
obj object to query
Return value
the MonoClass of the object.
Description
Use this function to obtain the MonoClass* for a given MonoObject.
mono_object_get_domain
Syntax
MonoDomain* mono_object_get_domain (MonoObject *obj)

Parameters
obj object to query
Return value
the MonoDomain where the object is hosted
mono_object_get_virtual_method
Syntax
MonoMethod* mono_object_get_virtual_method (MonoObject *obj, MonoMethod *method)

Parameters
obj object to operate on.
method method
Description
Retrieves the MonoMethod that would be called on obj if obj is passed as the instance of a callvirt of method.
mono_object_isinst_mbyref
Syntax
MonoObject* mono_object_isinst_mbyref (MonoObject *obj_raw, MonoClass *klass)

mono_object_isinst
Syntax
MonoObject* mono_object_isinst (MonoObject *obj_raw, MonoClass *klass)

Parameters
obj an object
klass a pointer to a class
Return value
obj if obj is derived from klass or NULL otherwise.
mono_object_unbox
Syntax
void* mono_object_unbox (MonoObject *obj)

Parameters
obj object to unbox
Return value
a pointer to the start of the valuetype boxed in this object.

This method will assert if the object passed is not a valuetype.

mono_object_castclass_mbyref
Syntax
MonoObject* mono_object_castclass_mbyref (MonoObject *obj_raw, MonoClass *klass)

Parameters
obj an object
klass a pointer to a class
Return value
obj if obj is derived from klass, returns NULL otherwise.
mono_object_get_size
Syntax
unsigned mono_object_get_size (MonoObject *o)

Parameters
o object to query
Return value
the size, in bytes, of o
mono_object_hash
Syntax
mono_object_hash

mono_object_to_string
Syntax
MonoString* mono_object_to_string (MonoObject *obj, MonoObject **exc)

Parameters
obj The object
exc Any exception thrown by ToString. May be NULL.
Return value
the result of calling ToString on an object.

Value Types

mono_value_box
Syntax
MonoObject* mono_value_box (MonoDomain *domain, MonoClass *klass, gpointer value)

Parameters
class the class of the value
value a pointer to the unboxed data
Return value
A newly created object which contains value.
mono_value_copy
Syntax
void mono_value_copy (gpointer dest, gpointer src, MonoClass *klass)

Parameters
dest destination pointer
src source pointer
klass a valuetype class
Description
Copy a valuetype from src to dest. This function must be used when klass contains reference fields.
mono_value_copy_array
Syntax
void mono_value_copy_array (MonoArray *dest, int dest_idx, void* src, int count)

Parameters
dest destination array
dest_idx index in the dest array
src source pointer
count number of items
Description
Copy count valuetype items from src to the array dest at index dest_idx. This function must be used when klass contains references fields. Overlap is handled.

Array Methods

Use the mono_array_new_* methods to create arrays of a given type.

For example, the following code creates an array with two elements of type System.Byte, and sets the values 0xca and 0xfe on it: 

MonoArray *CreateByteArray (MonoDomain *domain)
{
    MonoArray *data;

    data = mono_array_new (domain, mono_get_byte_class (), 2);
    mono_array_set (data, guint8, 0, 0xca);
    mono_array_set (data, guint8, 0, 0xfe);

    return data;
}

Creating Arrays

mono_array_new
Syntax
MonoArray* mono_array_new (MonoDomain *domain, MonoClass *eclass, uintptr_t n)

Parameters
domain domain where the object is created
eclass element class
n number of array elements
Description
This routine creates a new szarray with n elements of type eclass.
mono_array_new_full
Syntax
MonoArray* mono_array_new_full (MonoDomain *domain, MonoClass *array_class, uintptr_t *lengths, intptr_t *lower_bounds)

Parameters
domain domain where the object is created
array_class array class
lengths lengths for each dimension in the array
lower_bounds lower bounds for each dimension in the array (may be NULL)
Description
This routine creates a new array object with the given dimensions, lower bounds and type.
mono_array_new_specific
Syntax
MonoArray* mono_array_new_specific (MonoVTable *vtable, uintptr_t n)

Parameters
vtable a vtable in the appropriate domain for an initialized class
n number of array elements
Description
This routine is a fast alternative to mono_array_new for code which can be sure about the domain it operates in.
mono_array_class_get
Syntax
MonoClass* mono_array_class_get (MonoClass *eclass, guint32 rank)

Parameters
element_class element class
rank the dimension of the array class
Return value
A class object describing the array with element type element_type and dimension rank.
mono_array_clone
Syntax
MonoArray* mono_array_clone (MonoArray *array)

Parameters
array the array to clone
Return value
A newly created array who is a shallow copy of array

Using Arrays

Arrays are represented by the `MonoArray` data type and are instances of `MonoObject`. While you can use the `bounds` and `max_length` fields of the type, the actual storage (represented by `vector`) is not very useful. Instead you should use one of the accesor methods described below to fetch or set the values in the array.

When setting values in an array, you should use mono_array_set for setting elements in an array that contains value types, and mono_array_setref for arrays that contain reference types.

The mono_array_get, mono_array_set and mono_array_setref are C macros that wrap the underlying array access.

mono_array_get
Syntax
Type mono_array_get_internal (MonoArray *array, Type element_type, uintptr_t index)

Parameters
array array on which to operate on
element_type C element type (example: MonoString*, int, MonoObject*)
index index into the array
Return value
The element at the index position in the array.
Description

Use this macro to retrieve the index element of an array and extract the value assuming that the elements of the array match the provided type value.

This method can be used with both arrays holding value types and reference types. For reference types, the type parameter should be a MonoObject* or any subclass of it, like MonoString*.

This macro does not attempt to perform type checking or bounds checking.

mono_array_length
Syntax
uintptr_t mono_array_length (MonoArray *array)

Parameters
array a MonoArray*
Return value
the total number of elements in the array. This works for both vectors and multidimensional arrays.
mono_array_set
Syntax
void mono_array_set(MonoArray *array, Type element_type, uintptr_t index, Value value)

Parameters
array array to alter
element_type A C type name, this macro will use the sizeof(type) to determine the element size
index index into the array
value value to set
version This sets the index's element of the array
Description
with elements of size sizeof(type) to the provided value.

This macro does not attempt to perform type checking or bounds checking and it doesn't execute any write barriers.

Use this to set value types in a MonoArray. This shouldn't be used if the copied value types contain references. Use mono_gc_wbarrier_value_copy instead when also copying references.

mono_array_setref
Syntax
void mono_array_setref(MonoArray *array, uintptr_t index, MonoObject *object)

Parameters
array array to alter
index index into the array
value value to set
Description
Reference Type version. This sets the index's element of the array with elements of size sizeof(type) to the provided value.

This macro does not attempt to perform type checking or bounds checking.

Use this to reference types in a MonoArray.

mono_array_addr
Syntax
mono_array_addr

mono_array_addr_with_size
Syntax
char* mono_array_addr_with_size (MonoArray *array, int size, uintptr_t idx)

Parameters
array a MonoArray*
size size of the array elements
idx index into the array
Return value
the address of the idx element in the array.
Description
Use this function to obtain the address for the idx item on the array containing elements of size size.

This method performs no bounds checking or type checking.

mono_array_element_size
Syntax
gint32 mono_array_element_size (MonoClass *ac)

Parameters
ac pointer to a MonoArrayClass
Return value
The size of single array element.

LOCKING: Acquires the loader lock.

Description

Fields

mono_field_from_token

Deprecated: use the _checked variant
Syntax
MonoClassField* mono_field_from_token (MonoImage *image, guint32 token, MonoClass **retklass, MonoGenericContext *context)

Parameters
Notes runtime code MUST not use this function
mono_field_get_flags
Syntax
mono_field_get_flags

mono_field_get_name
Syntax
const char* mono_field_get_name (MonoClassField *field)

Parameters
field the MonoClassField to act on
Return value
The name of the field.
Description

mono_field_get_parent
Syntax
MonoClass* mono_field_get_parent (MonoClassField *field)

Parameters
field the MonoClassField to act on
Return value
MonoClass where the field was defined.
Description

mono_field_get_type
Syntax
MonoType* mono_field_get_type (MonoClassField *field)

Parameters
field the MonoClassField to act on
Return value
MonoType of the field.
mono_field_get_value
Syntax
void mono_field_get_value (MonoObject *obj, MonoClassField *field, void *value)

Parameters
obj Object instance
field MonoClassField describing the field to fetch information from
value pointer to the location where the value will be stored
Description
Use this routine to get the value of the field field in the object passed.

The pointer provided by value must be of the field type, for reference types this is a MonoObject*, for value types its the actual pointer to the value type.

For example: 

 int i;


 mono_field_get_value (obj, int_field, &i);
mono_field_get_value_object
Syntax
MonoObject* mono_field_get_value_object (MonoDomain *domain, MonoClassField *field, MonoObject *obj)

Parameters
domain domain where the object will be created (if boxing)
field MonoClassField describing the field to fetch information from
obj The object instance for the field.
Return value
a new MonoObject with the value from the given field. If the field represents a value type, the value is boxed.
mono_field_set_value
Syntax
void mono_field_set_value (MonoObject *obj, MonoClassField *field, void *value)

Parameters
obj Instance object
field MonoClassField describing the field to set
value The value to be set
Description

Sets the value of the field described by field in the object instance obj to the value passed in value. This method should only be used for instance fields. For static fields, use mono_field_static_set_value.

The value must be in the native format of the field type.

mono_field_static_get_value
Syntax
void mono_field_static_get_value (MonoVTable *vt, MonoClassField *field, void *value)

Parameters
vt vtable to the object
field MonoClassField describing the field to fetch information from
value where the value is returned
Description
Use this routine to get the value of the static field field value.

The pointer provided by value must be of the field type, for reference types this is a MonoObject*, for value types its the actual pointer to the value type.

For example: 

     int i;


     mono_field_static_get_value (vt, int_field, &i);
mono_field_static_set_value
Syntax
void mono_field_static_set_value (MonoVTable *vt, MonoClassField *field, void *value)

Parameters
field MonoClassField describing the field to set
value The value to be set
Description
Sets the value of the static field described by field to the value passed in value. The value must be in the native format of the field type.
mono_field_get_object
Syntax
MonoReflectionField* mono_field_get_object (MonoDomain *domain, MonoClass *klass, MonoClassField *field)

Parameters
domain an app domain
klass a type
field a field
Return value
A System.Reflection.MonoField object representing the field field in class klass.

Properties

mono_property_get_object
Syntax
MonoReflectionProperty* mono_property_get_object_checked (MonoDomain *domain, MonoClass *klass, MonoProperty *property, MonoError *error)

Parameters
domain an app domain
klass a type
property a property
error set on error
Return value
a System.Reflection.MonoProperty object representing the property property in class klass. On error returns NULL and sets error.
mono_property_get_flags
Syntax
guint32 mono_property_get_flags (MonoProperty *prop)

Parameters
prop the MonoProperty to act on.
Return value
The flags for the property.
Description

The metadata flags for a property are encoded using the PROPERTY_ATTRIBUTE_* constants. See the tabledefs.h file for details.

mono_property_get_get_method
Syntax
MonoMethod* mono_property_get_get_method (MonoProperty *prop)

Parameters
prop the MonoProperty to act on.
Return value
The getter method of the property (A MonoMethod)
mono_property_get_name
Syntax
mono_property_get_name

mono_property_get_parent
Syntax
MonoClass* mono_property_get_parent (MonoProperty *prop)

Parameters
prop the MonoProperty to act on.
Return value
The MonoClass where the property was defined.
mono_property_get_set_method
Syntax
MonoMethod* mono_property_get_set_method (MonoProperty *prop)

Parameters
prop the MonoProperty to act on.
Return value
The setter method of the property, a MonoMethod.
mono_property_get_value
Syntax
MonoObject* mono_property_get_value (MonoProperty *prop, void *obj, void **params, MonoObject **exc)

Parameters
prop MonoProperty to fetch
obj instance object on which to act
params parameters to pass to the propery
exc optional exception
Return value
the value from invoking the get method on the property.
Description
Invokes the property's get method with the given arguments on the object instance obj (or NULL for static properties).

You can pass NULL as the exc argument if you don't want to catch exceptions, otherwise, *exc will be set to the exception thrown, if any. if an exception is thrown, you can't use the MonoObject* result from the function.

mono_property_set_value
Syntax
void mono_property_set_value (MonoProperty *prop, void *obj, void **params, MonoObject **exc)

Parameters
prop MonoProperty to set
obj instance object on which to act
params parameters to pass to the propery
exc optional exception
Description
Invokes the property's set method with the given arguments on the object instance obj (or NULL for static properties).

You can pass NULL as the exc argument if you don't want to catch exceptions, otherwise, *exc will be set to the exception thrown, if any. if an exception is thrown, you can't use the MonoObject* result from the function.

Events

mono_event_get_object
Syntax
MonoReflectionEvent* mono_event_get_object (MonoDomain *domain, MonoClass *klass, MonoEvent *event)

Parameters
domain an app domain
klass a type
event a event
Return value
A System.Reflection.MonoEvent object representing the event event in class klass.
mono_event_get_add_method
Syntax
MonoMethod* mono_event_get_add_method (MonoEvent *event)

Parameters
event The MonoEvent to act on.
Return value
The add method for the event, a MonoMethod.
mono_event_get_flags
Syntax
guint32 mono_event_get_flags (MonoEvent *event)

Parameters
event the MonoEvent to act on.
Return value
The flags for the event.
Description

The metadata flags for an event are encoded using the EVENT_* constants. See the tabledefs.h file for details.

mono_event_get_name
Syntax
const char* mono_event_get_name (MonoEvent *event)

Parameters
event the MonoEvent to act on
Return value
The name of the event.
mono_event_get_parent
Syntax
MonoClass* mono_event_get_parent (MonoEvent *event)

Parameters
event the MonoEvent to act on.
Return value
The MonoClass where the event is defined.
mono_event_get_raise_method
Syntax
MonoMethod* mono_event_get_raise_method (MonoEvent *event)

Parameters
event The MonoEvent to act on.
Return value
The raise method for the event, a MonoMethod.
mono_event_get_remove_method
Syntax
MonoMethod* mono_event_get_remove_method (MonoEvent *event)

Parameters
event The MonoEvent to act on.
Return value
The remove method for the event, a MonoMethod.

Remote Fields

mono_load_remote_field
Syntax
gpointer mono_load_remote_field (MonoObject *this_obj, MonoClass *klass, MonoClassField *field, gpointer *res)

Parameters
this pointer to an object
klass klass of the object containing field
field the field to load
res a storage to store the result
Return value
an address pointing to the value of field.
Description
This method is called by the runtime on attempts to load fields of transparent proxy objects. this points to such TP, klass is the class of the object containing field. res is a storage location which can be used to store the result.
mono_load_remote_field_new
Syntax
MonoObject* mono_load_remote_field_new (MonoObject *this_obj, MonoClass *klass, MonoClassField *field)

Parameters
this
klass
field
Description
Missing documentation.
mono_store_remote_field
Syntax
void mono_store_remote_field (MonoObject *this_obj, MonoClass *klass, MonoClassField *field, gpointer val)

Parameters
this_obj pointer to an object
klass klass of the object containing field
field the field to load
val the value/object to store
Description
This method is called by the runtime on attempts to store fields of transparent proxy objects. this_obj points to such TP, klass is the class of the object containing field. val is the new value to store in field.
mono_store_remote_field_new
Syntax
void mono_store_remote_field_new (MonoObject *this_obj, MonoClass *klass, MonoClassField *field, MonoObject *arg)

Parameters
this_obj
klass
field
arg
Description
Missing documentation

Delegates

mono_get_delegate_begin_invoke
Syntax
MonoMethod* mono_get_delegate_begin_invoke (MonoClass *klass)

Parameters
klass The delegate class
Return value
the MonoMethod for the BeginInvoke method in the delegate class or NULL if klass is a broken delegate type