Why invariants in D 2.0 std.string?

[David B. Held]

Nathan Reed wrote:
> Janice Caron wrote:
>> I kinda like that.
>>
>> I imagine the reasoning is that the library functions will go faster,
>> because they can be optimised better.
> 
> How does invariant allow better optimization than const?
> [...]

A const string may be intrinsically mutable but you only have a 
read-only view of it.  An invariant string is intrinsically immutable, 
so you can make extra assumptions about what it won't do while you poke it.

Dave