Does foreach copy each element if it is an array of structs?

.net, c#

Solution

Yes, copies of the value type instances will be made. When iterating over an array, `foreach` will indeed use array accesses instead of using an enumerator, but the value in each array slot is still copied.

This code:

struct AStruct
{
    public string a;
    public int b;

    static void Main()
    {
        var structs = new AStruct[10];

        foreach (var x in structs) {
            Console.WriteLine(x);
        }
    }
}

Generates the following IL for the `Main()` method:

.method private static hidebysig
       default void Main ()  cil managed
{
    .entrypoint
    .maxstack 4
    .locals init (
            valuetype AStruct[]     V_0,
            valuetype AStruct[]     V_1,
            int32   V_2,
            valuetype AStruct       V_3)
    IL_0000:  ldc.i4.s 0x0a
    IL_0002:  newarr AStruct
    IL_0007:  stloc.0
    IL_0008:  ldloc.0
    IL_0009:  stloc.1
    IL_000a:  ldc.i4.0
    IL_000b:  stloc.2
    IL_000c:  br IL_002d

    IL_0011:  ldloc.1
    IL_0012:  ldloc.2
    IL_0013:  ldelema AStruct
    IL_0018:  ldobj AStruct
    IL_001d:  stloc.3
    IL_001e:  ldloc.3
    IL_001f:  box AStruct
    IL_0024:  call void class [mscorlib]System.Console::WriteLine(object)
    IL_0029:  ldloc.2
    IL_002a:  ldc.i4.1
    IL_002b:  add
    IL_002c:  stloc.2
    IL_002d:  ldloc.2
    IL_002e:  ldloc.1
    IL_002f:  ldlen
    IL_0030:  conv.i4
    IL_0031:  blt IL_0011

    IL_0036:  ret
} // end of method AStruct::Main

Note the instructions IL_0013 through IL_001d. The entire value at each array slot is pushed onto the stack and stored in the local V_3 (the `x` iteration variable).

Problem

I have an array of structs. Does `foreach` operator make a copy of each element when iterating thru an array? As far as I understand `foreach` is just syntactic sugar under the hood converted to `for`. So it appears the answer is no but I'd love to have some confirmation. PS: it appears someone should have already asked that but I can't easily find anything. So please vote as a dup with provided reference.

Original source