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There's a few challenges with doing something like this. - arrays (which most collections use under the covers) will need to allocate `elements*size_of_struct`

There's a few challenges with doing something like this. - arrays (which most collections use under the covers) will need to allocate `elements*size_of_struct`. Unless the structs are the same size, you'd have to do some level of thunking/offsetting. - Even if they are the same size, when you're iterating the list, how would the runtime know whether it's `A`, `B`, or `C`? Structs don't have header information that can be used to infer the type, it's only whatever fields you've defined (with padding potentially). Part of 'boxing' is essentially thunking the struct by wrapping a methodtable for the struct into the object [0]. If you need something like polymorphism with structs, your best bet is to make the struct itself quasi-polymorphic (i.e. with enums) and/or start abusing generics in some fashion I haven't yet figured out. [0] - https://mattwarren.org/2017/08/02/A-look-at-the-internals-of-boxing-in-the-CLR/ https://mattwarren.org/2017/08/02/A-look-at-the-internals-of...

Ygg2 6y ago
> Structs don't have header information that can be used to infer the type, it's only whatever fields you've defined (with padding potentially). Sure, so let's make union or "struct enum" and do the same thing Rust does. Add a discriminator byte to the structure and use it to figure out type. > If you need something like polymorphism with structs, your best bet is to make the struct itself quasi-polymorphic (i.e. with enums) and/or start abusing generics in some fashion I haven't yet figured out. Well. I think there is the FieldOffset hack. Basically discriminated unions where programmer plays the role of compiler. [StructLayout(LayoutKind.Explicit)] struct DiscriminatedUnion { // Imagine we have enum like so // enum // { // V1(byte a, byte b) // V2(sbyte a, sbyte b) // } // The "FieldOffset" means that this Integer starts, an offset in bytes. // sizeof(byte) = 1, sizeof(EnumType) = 1 [FieldOffset(0)] public EnumType TypeFlag; [FieldOffset(1)] public byte V1a; [FieldOffset(2)] public byte V1b; [FieldOffset(1)] public sbyte V2a; [FieldOffset(2)] public sbyte V2b; } https://sodocumentation.net/csharp/topic/5626/how-to-use-csharp-structs-to-create-a-union-type---similar-to-c-unions- https://sodocumentation.net/csharp/topic/5626/how-to-use-csh... Problem is, this is fragile. It might break on endianess.

Ygg2 6y ago

> Structs don't have header information that can be used to infer the type, it's only whatever fields you've defined (with padding potentially). Sure, so let's make union or "struct enum" and do the same thing Rust does. Add a discriminator byte to the structure and use it to figure out type. > If you need something like polymorphism with structs, your best bet is to make the struct itself quasi-polymorphic (i.e. with enums) and/or start abusing generics in some fashion I haven't yet figured out. Well. I think there is the FieldOffset hack. Basically discriminated unions where programmer plays the role of compiler. [StructLayout(LayoutKind.Explicit)] struct DiscriminatedUnion { // Imagine we have enum like so // enum // { // V1(byte a, byte b) // V2(sbyte a, sbyte b) // } // The "FieldOffset" means that this Integer starts, an offset in bytes. // sizeof(byte) = 1, sizeof(EnumType) = 1 [FieldOffset(0)] public EnumType TypeFlag; [FieldOffset(1)] public byte V1a; [FieldOffset(2)] public byte V1b; [FieldOffset(1)] public sbyte V2a; [FieldOffset(2)] public sbyte V2b; } https://sodocumentation.net/csharp/topic/5626/how-to-use-csharp-structs-to-create-a-union-type---similar-to-c-unions- https://sodocumentation.net/csharp/topic/5626/how-to-use-csh... Problem is, this is fragile. It might break on endianess.