Julia Language String Macros Symbols that are not legal identifiers
Example
Julia Symbol literals must be legal identifiers. This works:
julia> :cat
:cat
But this does not:
julia> :2cat
ERROR: MethodError: no method matching *(::Int64, ::Base.#cat)
Closest candidates are:
*(::Any, ::Any, ::Any, ::Any...) at operators.jl:288
*{T<:Union{Int128,Int16,Int32,Int64,Int8,UInt128,UInt16,UInt32,UInt64,UInt8}}(::T<:Union{Int128,Int16,Int32,Int64,Int8,UInt128,UInt16,UInt32,UInt64,UInt8}, ::T<:Union{Int128,Int16,Int32,Int64,Int8,UInt128,UInt16,UInt32,UInt64,UInt8}) at int.jl:33
*(::Real, ::Complex{Bool}) at complex.jl:180
...
What looks like a symbol literal here is actually being parsed as an implicit multiplication of :2 (which is just 2) and the function cat, which obviously does not work.
We can use
julia> Symbol("2cat")
Symbol("2cat")
to work around the issue.
A string macro could help to make this more terse. If we define the @sym_str macro:
macro sym_str(str)
Meta.quot(Symbol(str))
end
then we can simply do
julia> sym"2cat"
Symbol("2cat")
to create symbols which are not valid Julia identifiers.
Of course, these techniques can also create symbols that are valid Julia identifiers. For example,
julia> sym"test"
:test
