intern/cache array instances created via collection expressions when the contents are literal/constant

[alex-jitbit]

Consider this code:

string[] myArray = ["a", "b", "c"];

It's immutable and all contents is known at compile time.

The compiler should maybe "intern" this? Emit as a static variable?

[RikkiGibson]

string[] is mutable, so the compiler wouldn't be able to reuse the value created for this collection-expression.

We do have a sort of "caching" today for collection expressions of certain ReadOnlySpans, when the element type is an unmanaged built-in, like bool, int, or byte, and the elements are constants. In that case we give a span into the assembly's data segment.

We could consider an expanded "caching" optimization for collection expressions targeting "read-only" types.

[huoyaoyuan]

It's not something addressable for C# compiler. Mutation can easily happen when the array is passed to a different method.

If it's provable to be immutable, then it must be non-escaping, then the JIT compiler can cancel the array object itself.