`getproperty` with other types than `Symbol`

General Usage
1

I noticed that one can overload getproperty with String, not only Symbol (PyCall does this):

julia> struct Foo end

julia> import Base: getproperty

julia> getproperty(::Foo, x::Symbol) = x
getproperty (generic function with 22 methods)

julia> getproperty(::Foo, x::String) = x
getproperty (generic function with 23 methods)

julia> Foo().sdf
:sdf

julia> Foo()."sdf"
"sdf"

But it doesn’t work with, e.g., integers (this is even a parse error):

julia> getproperty(::Foo, x::Int) = x
getproperty (generic function with 24 methods)

julia> Foo().1
ERROR: syntax: extra token "0.1" after end of expression
Stacktrace:
 [1] top-level scope at REPL[11]:0

Is there any documentation about what types can (or should) be used?

2

The getproperty docstring seems to document usage only with symbols. In the integers case, you can quote them, e.g. Foo().:1 .

3

Ah, that’s a good hint. Apparently, you can use any literals, as long as you quote them:

julia> Foo().:true
ERROR: MethodError: no method matching getproperty(::Foo, ::Bool)
Closest candidates are:
  getproperty(::Foo, ::Foo) at REPL[13]:1
  getproperty(::Foo, ::Int64) at REPL[11]:1
  getproperty(::Foo, ::String) at REPL[8]:1
  ...

Although there are some strange corner cases from the parser – the following two count as “just” symbols:

julia> Foo().:nothing
:nothing

julia> Foo().:notsdf
:notsdf
4

Note that :true === true, like for integers a quoted Bool is equal to itself. But Foo().true can work directly, as there is no parser ambiguity like with Foo().1. On the other hand, :nothing is a Symbol, i.e. :nothing !== nothing.