class Type1
{
    // This parameter will have an attribute (in IL) of type `IsReadOnly`
    public void Method1(ref readonly int param1) { throw null; }

    // This method return type will have an attribute (in IL) of type `IsReadOnly`
    public ref readonly int Method2() { throw null; }
}

VC>class Type1
VC>{
VC>    // This parameter will have an attribute (in IL) of type `IsReadOnly`
VC>    public void Method1(ref readonly int param1) { throw null; }

VC>    // This method return type will have an attribute (in IL) of type `IsReadOnly`
VC>    public ref readonly int Method2() { throw null; }
VC>}
VC>

const int *

VC>А зачем нижний (return)? Туплю

VC>Если можно пример парами — как раньше делалось и как теперь это готовить

VC>И зачем оно в IL нужно, можно же было только си-шарпом обойтись

ref byte x = span[1];
// (псевдокод)
.ldelema array span_offset+1

ref char x = stringSpan[1];
x = 'X'; // oops

Represents a weak reference, which references an object while still allowing that object to be reclaimed by garbage collection.

class Type1
{
    private int _myInt = 42;

    // This method return type will have an attribute (in IL) of type `IsReadOnly`
    public ref readonly int Method2() { return ref this._myInt; }
    public WeakReference<int> OldSchoolMethod2() { return new WeakReference<int>(this._myInt); }
}

...

var t = new Type1();
ref int x = t.Method2(); // будет ли это влиять на GC?
WeakReference<int> y = t.OldSchoolMethod2(); // потому что это - не должно (y.Target==null после сборки мусора)

Since all regular instance methods of a struct can potentially mutate the instance or ref-expose this, an intermediate copy must be created, as already a case when receiver is a readonly field.

readonly ref int Min(readonly ref int a, readonly ref int b)
{
   if (a < b) return ref a;
   return ref b;
}

readonly T Min(readonly T a, readonly T b)
{
    if(a.CompareTo(b) <= 0)
        return a;
    else
        return b;
}

_>readonly T Min(readonly T a, readonly T b)
_>{
_>    if(a.CompareTo(b) <= 0)
_>        return a;
_>    else
_>        return b;
_>}
_>

var array = new []{1, 2};

ref int min = Min(ref array[0], ref array[1]); // не уверен за синтаксис

array[0] = 100;
Console.WriteLine(min);