add to Unsafe.SkipInit , support for ref struct items

[irvnriir]

due to that ref struct can't be used as Generic 's Type Parameter, Unsafe.SkipInit doesn't work for it .

[huoyaoyuan]

Generic parameter support for ref struct is #1148.
Unsafe.SkipInit won't take effect for ref struct, since it can contain ref field, and it usually does contain.

[irvnriir]

this is not a suggestion for allowing general use as Generic parameter .

i do not see how this is related to ref fields .

[huoyaoyuan]

Unsafe.SkipInit is not known by the language. It is just a runtime-provided helper. Without generic parameter support, such helper can't be defined for ref structs.

Ref fields and reference type fields must be initialized to null since GC can't handle wild references.

[irvnriir]

i thought it has specific handling by compiler, to not error due to that it has not Definition for it's out parameter, and to avoid providing excessive output . dotnet/runtime#29905 .

They don't exist until the struct is initialized, why/how would GC interact with them ?

[huoyaoyuan]

The definition order of a variable in source language is almost unrelated to the lifetime of its runtime representation. out variable definition is just a syntax sugar. You can see the compilation results to be undistinguishable.

[irvnriir]

If you mean that following not existing references is unsafe, thats the same for the struct itself .

[irvnriir]

#7581 (reply in thread)

ik that, but don't see how its related