On 2016-11-07 17:48, John Colvin wrote:
Some people use ref for performance to prevent the copying that must occur when passing by value. I propose a small optimisation to make this unnecessary in a bunch of cases.At the ABI level (no change in language semantics), if a given parameter would otherwise be copied and passed on the stack: 1) immutable parameters to all functions are passed by reference 2) const parameters to pure functions are passed by reference, if and only if all other parameters - including any implicit this parameter - contain no mutable references (otherwise "weakly" pure functions could modify the data we are now referring to instead of having copied, changing semantics). The main benefit from this would be: class C { void doSomething(const float[16] m0) const pure { // ... } void doSomethingElse(immutable float[16] m1) { // ... } } void foo(C c, float[16] m0, immutable float[16] m1) { // ... c.doSomething(m0); // no copying of m0 here c.doSomethingElse(m1); // or m1 here // ... } I presume this has been thought of before, is there a reason why we don't do it already? I guess 2) is a bit complicated, but 1) is easy.
Since D is a systems programming language, wouldn't the user want to have control over this?
-- /Jacob Carlborg
