Why this parametric constructor only works with multiline definition? - julia

Question

I have a Device constructor that only works if I define it using the multiline function syntax, but it fails if I define it with the one line function syntax, with the following error:
ERROR: LoadError: UndefVarError: F not defined (if I remove F) or
ERROR: LoadError: UndefVarError: C not defined
However it also works if I only remove the F and C type parameters from the method signature (but not the where {C<:UxnCpu, F<:Function} part).
69 abstract type AbstractCPU end
70 mutable struct Device{C<:AbstractCPU, F<:Function}
71 cpu::C
72 id_addr::Int
73 vector::UInt16
74 talk::F
75 mem::OVector{UInt8}
76 dat::OVector{UInt8}
77 end
78
79 function Device(cpu::C, id_addr::Int, talkfn::F)::Device where {C<:AbstractCPU, F<:Function}
80 d = Device(cpu, id_addr, 0x000, talkfn, cpu.ram.dat, OVector{UInt8}(0x10))
81 cpu.dev[id_addr] = d
82
83 return d
84 end
85
---> 86 Device(talkfn::F, cpu::C, id_addr::Int)::Device where {C<:AbstractCPU, F<:Function} = Device(cpu, id_addr, talkfn)
87
88 Device(cpu, id_addr::Int) where {C<:AbstractCPU} = begin
89 Device(cpu, id_addr) do d::Device, b0::UInt8, w::UInt8
90 return true
91 end
92 end
The full stack trace is:
ERROR: LoadError: UndefVarError: F not defined
Stacktrace:
[1] top-level scope
# C:\Users\ismae\Bin\uxn-dev\src\VarvaraEmulator.jl:86 <---
[2] include(fname::String)
# Base.MainInclude .\client.jl:444
[3] top-level scope
# REPL[6]:1
in expression starting at C:\Users\ismae\Bin\uxn-dev\src\VarvaraEmulator.jl:25
However this workarounds do work:
Device(talkfn, cpu, id_addr::Int)::Device where {C<:AbstractCPU, F<:Function} = Device(cpu, id_addr, talkfn)
I would have thought it would complain with something about to few type parameters in signature.
The following syntax doesn't work either:
Device(talkfn::F, cpu::C, id_addr::Int)::Device where {C<:AbstractCPU, F<:Function} = begin
Device(cpu, id_addr, talkfn)
end
However this does, which is what I left in the end:
function Device(talkfn::F, cpu::C, id_addr::Int)::Device where {C<:AbstractCPU, F<:Function}
Device(cpu, id_addr, talkfn)
end
I would like to understand where that error is coming from, what am I doing wrong?
I tried to replicate it in a minimal example, but I was not able to, here is my the complete code for reference:
https://github.com/Ismael-VC/VarvaraEmulator.jl/blob/VarvaraEmulator.jl/src/VarvaraEmulator.jl#L69-L99
This is my current setup:
julia> versioninfo()
Julia Version 1.6.3
Commit ae8452a9e0 (2021-09-23 17:34 UTC)
Platform Info:
OS: Windows (x86_64-w64-mingw32)
CPU: Intel(R) Core(TM) i7-4710HQ CPU # 2.50GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-11.0.1 (ORCJIT, haswell)
Environment:
JULIA_LOAD_PATH = C:\Users\\smae\Bin\uxn-dev\src;
(#v1.6) pkg> status
Status `C:\Users\ismae\.julia\environments\v1.6\Project.toml`
[6e4b80f9] BenchmarkTools v1.2.0
[c43c736e] Genie v3.2.0
[7eb4fadd] Match v1.1.0
[6fe1bfb0] OffsetArrays v1.10.7
[c3e4b0f8] Pluto v0.16.1
[b873ce64] ReplMaker v0.2.5
[98e33af6] SimpleDirectMediaLayer v0.3.0
[90137ffa] StaticArrays v1.2.13
Best regards.

Answer 1

I think it's just an issue parsing the parameters when there is a return type annotation, not your fault. I can replicate the error with a much more minimal example.
These work:
function f1(x::F, y::C) where {F<:Integer, C<:Complex}
1
end
function f2(x::F, y::C)::Int where {F<:Integer, C<:Complex}
2
end
g1(x::F, y::C) where {F<:Integer, C<:Complex} = 3
But this doesn't:
g2(x::F, y::C)::Int where {F<:Integer, C<:Complex} = 4
Edit: From the comments, the last case can be fixed by adding parentheses:
(g2(x::F, y::C)::Int) where {F<:Integer, C<:Complex} = 4