Why C# builtin types contain implementation?

Question

It's a known fact builtin types like Int32/Double/... are implemented on compiler level, and users cannot implement recursive structs like Int32:

public readonly struct Int32 : IComparable, IConvertible, IFormattable, IComparable<int>, IEquatable<int>, ISpanFormattable
{
    private readonly int m_value; // Do not rename (binary serialization)

Considering int to be an alias to Int32 we have an unsolvable recursion here. But it's fine since it get compiler's "special comprehension".

However, I wonder why it contains any implementation at all. If you look at the file you can see that there is code that real runtime seems to actually use.

I wonder why bultin types are not just stubs? I firstly imagined that it may be used as implementation of the boxed value, but it doesn't work to me since it's declared as struct. However, with compiler black magic everything becomes possible. But I don't know for sure.

The actual built-in (primitive) types are _mapped_ to the library types. They are not 'implemented' by them. — bommelding, Jan 09 '19 at 12:07
@bommelding ECMA334/335 treat them as aliases so they are precisely the same thing — Alex Zhukovskiy, Jan 09 '19 at 13:39
My concern is that you can't write `struct MyInt32 { private MyInt32 m_value; }`, but compiler do it here since `typeof(int) == typeof(Int32)` — Alex Zhukovskiy, Jan 09 '19 at 13:40
I would indeed write that off as compiler magic. In general, you can't create a primitive type. — bommelding, Jan 09 '19 at 13:47
It seems like a smart design to do that. Runtime magic is always more work and more brittle. Write as much code in C# as possible. — usr, Jan 09 '19 at 14:24
Possible duplicate of [System.Int32 contains... another System.Int32](https://stackoverflow.com/questions/3375165/system-int32-contains-another-system-int32) — MulleDK19, Sep 29 '19 at 18:11

Why C# builtin types contain implementation?

0 Answers0