Switch from vecn function to vecn! macro

[bitshifter]

It might be more useful if functions like vec2, vec3, mat2 etc became macros as then they could support different parameter types, e.g.

• vec4!(1.0, 2.0, 3.0, 4.0) - regular construction
• vec4![1.0, 2.0, 3.0, 4.0] or vec4![2.0; 4] - array construction
• vec4!(3.0) - splat from a scalar

It might mean these are a bit more useful than the currently are.

[Boscop]

Yeah, that would be useful.
Also vec3!(vec2!(1.0, 2.0), 3.0), vec3!(3.0, vec2!(1.0, 2.0)), vec4!(vec2!(1.0, 2.0), vec2!(3.0, 4.0)) etc.

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vec4![2.0; 4]

I don't think this one makes sense, the size is already expressed in the macro name, one would just call vec4!(2.0). But it would be useful to have an easy way to convert a [f32; 4] to Vec4.

[LPGhatguy]

Can the existing const macros be merged into the idea of these new macros? Is there a reason to keep const and non-const initialization separate?

As an intermediate step, would you be interested in merging the const macros with these functions to create new macros that are also const? It would be very nice to have a single shorthand for creating values.

The new macros could later be extended with scalar splat or array construction.

[bitshifter]

The const_vecn! macros are a workaround for limitations in Rust itself, see #76 for more details.

It might be possible to merge const_vecn! into vecn!. I'm not totally sure about doing that though, the const_vecn! does some hacky things (union casts) to be able to create a const value which possibly could produce worse code than the current vecn! macros which are simple inlined function calls. Technically it should be possible though. The only other reason to not do that is hopefully it's clear that the const_vecn! macros can be used to create const values. Without that naming it might not be obvious that vecn! can be used to create const values while the regular function VecN::new can not.

Long term if SIMD constructors in core::arch are made const fn the const_vecn macros will no longer be necessary.

[bitshifter]

Decided not to do this.