Composing types with non-concrete fields

Internals & Design
2

Any use of concrete fields should be fully optimizable no matter what is in the other fields.

julia> struct F
       a::Int
       b
       c
       d
       e
       end

julia> b = F(1,2,3,4,5)
F(1, 2, 3, 4, 5)

julia> f(A::F, B::F) = A.a + B.a
f (generic function with 1 method)

julia> @code_native f(b,b)
        .section        __TEXT,__text,regular,pure_instructions
; Function f {
; Location: REPL[33]:1
; Function +; {
; Location: REPL[33]:1
        movq    (%rsi), %rax
        addq    (%rdi), %rax
;}
        retq
        nopw    (%rax,%rax)
;}
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