2.4 KiB
Static Delegates
- Proposed
- Prototype: Not Started
- Implementation: Not Started
- Specification: Not Started
Summary
Provide a general-purpose, lightweight callback capability to the C# language.
Motivation
Today, users have the ability to create callbacks using the System.Delegate type. However, these are fairly heavyweight (such as requiring a heap allocation and always having handling for chaining callbacks together).
Additionally, System.Delegate does not provide the best interop with unmanaged function pointers, namely due being non-blittable and requiring marshalling anytime it crosses the managed/unmanaged boundary.
With a few minor tweaks, we could provide a new type of delegate that is lightweight, general-purpose, and interops well with native code.
Detailed design
One would declare a static delegate via the following:
static delegate int Func()
One could additionally attribute the declaration with something similar to System.Runtime.InteropServices.UnmanagedFunctionPointer so that the calling convention, string marshalling, and set last error behavior can be controlled. NOTE: Using System.Runtime.InteropServices.UnmanagedFunctionPointer itself will not work, as it is only usable on Delegates.
The declaration would get translated into an internal representation by the compiler that is similar to the following
struct <name>
{
IntPtr pFunction;
static int Func();
}
That is to say, it is internally represented by a struct that has a single member of type IntPtr (such a struct is blittable and does not incur any heap allocations). The member contains the address of the function that is to be the callback. Additionally, the type declares a method matching the method signature of the callback.
The value of the static delegate can only be bound to a static method that matches the signature of the callback.
Chaining callbacks together is not supported.
Invocation of the callback would be implemented by the calli instruction.
Drawbacks
TBD
Alternatives
TBD
Unresolved questions
What parts of the design are still TBD?
Design meetings
Link to design notes that affect this proposal, and describe in one sentence for each what changes they led to.