I've been working on a package Mocking.jl
<https://github.com/invenia/Mocking.jl> which allows developers to
temporarily overwrite a method in order to facilitate testing. I've got
everything working pretty well with the exception of the creation of a new
macro which is suppose to ensure that Julia doesn't inline or optimize the
call in such a way that the originally specified call can be overwritten:
julia> function myfunc(filename)
readall(open(filename))
end
myfunc (generic function with 1 method)
julia> myfunc("foo")
ERROR: SystemError: opening file foo: No such file or directory
in open at ./iostream.jl:90
in myfunc at none:2
julia> Base.open(name::AbstractString) = IOBuffer("bar")
WARNING: Method definition open(AbstractString) in module Base at
iostream.jl:99 overwritten in module Main at none:1.
open (generic function with 8 methods)
julia> myfunc("foo") # Open call within `myfunc` is not overwritten
ERROR: SystemError: opening file foo: No such file or directory
in open at ./iostream.jl:90
in myfunc at none:2
I can get this to work correctly with by adjusting the myfunc slightly:
julia> function myfunc(filename)
readall([open([filename]...)]...)
end
myfunc (generic function with 1 method)
julia> myfunc("foo")
ERROR: SystemError: opening file foo: No such file or directory
in open at ./iostream.jl:90
in open at iostream.jl:99
in myfunc at none:2
julia> Base.open(name::AbstractString) = IOBuffer("bar")
WARNING: Method definition open(AbstractString) in module Base at
iostream.jl:99 overwritten in module Main at none:1.
open (generic function with 8 methods)
julia> myfunc("foo")
"bar"
But this makes forces people to change their code and make it harder to
read. Not to mention that this is just fooling the compiler into getting
the behaviour I want. I would prefer to use a macro to get this behaviour
and I managed to get the following horrible macro to work:
julia> macro fix(ex)
name = gensym()
:(@generated function $name() $ex end; $name())
end
julia> function myfunc(filename)
@fix readall(open(filename))
end
myfunc (generic function with 1 method)
julia> myfunc("foo")
ERROR: SystemError: opening file foo: No such file or directory
in open at ./iostream.jl:90
in open at iostream.jl:99
in #2###6995 at none:3
in myfunc at none:2
julia> Base.open(name::AbstractString) = IOBuffer("bar")
WARNING: Method definition open(AbstractString) in module Base at
iostream.jl:99 overwritten in module Main at none:1.
open (generic function with 8 methods)
julia> myfunc("foo")
"bar"
Does anyone have any suggestions on how I can improve this macro and get
this behaviour? Bonus points if someone can tell me a good way of
determining if the macro is being called from within a `Pkg.test(...)`
process.
