I recently tried compiling enumap with GDC, and found that it
disagrees with DMD on whether a function is @nogc. Here's a
semi-reduced test-case:
---
import std.range;
import std.traits : EnumMembers;
import std.typecons : tuple, staticIota;
import std.algorithm : map;
struct Enumap(K, V)
if(EnumMembers!K == staticIota!(0, EnumMembers!K.length))
{
enum length = EnumMembers!K.length;
private V[length] _store;
ref auto opIndex(K key) inout {
return _store[key];
}
@nogc auto byKeyValue() const {
return only(EnumMembers!K).map!(key => tuple(key, this[key]));
}
}
@nogc void main() {
import std.typecons : tuple;
import std.algorithm : map;
enum E { a, b, c, d };
immutable elements = Enumap!(E, int)([1,2,3,4]);
auto pairs = elements.byKeyValue.map!(pair => tuple(pair[0],
pair[1] + 1));
}
---
GDC claims that byKeyValue() allocates a closure, but DMD is just
fine with me calling it @nogc. I'm inclined to agree with GDC
here, unless DMD is doing some magic so that actually doesn't
allocate a closure.
