Bug 21410 – idup of an array of immutable elements should be a no-op

string s = "foo"; assert(s.idup.ptr == s.ptr); // Fail If the data is immutable, it can already be assumed that it has infinite lifetime, so unless something is breaking the type system, it doesn't make sense to create another copy of it. The motivation is generic code such as the following: int[string] dict; void save(C : char)(C[] key, int value) { if (auto p = key in dict) *p = value; else dict[key.idup] = value; } This way, save can be called with either a char[] or string, and it will only copy the key argument if it needs to. Such a distinction can occur when e.g. deserializing data from memory (where it can be immutable), or chunk-wise from a stream (where the data's lifetime is only until the next chunk is read).

@CyberShadow created dlang/druntime pull request #3281 "Fix Issue 21410 - idup of an array of immutable elements should be a no-op" fixing this issue: - Fix Issue 21410 - idup of an array of immutable elements should be a no-op https://github.com/dlang/druntime/pull/3281

Closing as per the discussion in the PR.