Not really - you don't need to dispatch anything, the idea is that the same code (and thus the same assembly/machine code) can operate on different sizes by its

Not really - you don't need to dispatch anything, the idea is that the same code (and thus the same assembly/machine code) can operate on different sizes by itself. e.g. with RVV "vsetvli x0,x0,e32,m1,ta,ma; vadd.vv v0, v1, v2" on a CPU with 128-bit vectors will do 4 element additions, but on a CPU with 1024-bit vectors it'll do 32 additions. And some things you just can't really "generalize" to scalable vectors. e.g. you can store Simd<i32,4> in a struct or global variables, or initialize with, say, [3,2,1,0], but none of those things are possible with scalable vectors (globals/struct fields need a known size, and initializing with a hard-coded list of elements doesn't make much sense if you don't even know how many elements you'll need).