`std.heap.SmpAllocator` asserts `!builtin.single_threaded`

[leecannon]

Is there a good reason that SmpAllocator asserts not single threaded other than a different implementation might be more efficient in a single threaded situation?

I tried deleting the comptime assert and the allocator worked fine 🤷

zig/lib/std/heap/SmpAllocator.zig

Lines 113 to 115 in db622f1

	comptime {
	assert(!builtin.single_threaded); // you're holding it wrong
	}

[eamonburns]

zig/lib/std/heap/SmpAllocator.zig

Lines 1 to 2 in db622f1

	//! An allocator that is designed for ReleaseFast optimization mode, with
	//! multi-threading enabled.

Originally, I had thought this meant "built for Release fast, multi-threading supported", but now I think it means "built for ReleaseFast and multi-threading".

(I think the comma before the "with multi-threading" is technically grammatically incorrect in that case, but anyway 🤷‍♂️)