Cryptic error for Complex(::Irrational)

[malmaud]

julia> complex(pi)

ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Irrational{:π}

[mschauer]

That is

zero(pi)
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Irrational{:π}

[strickek]

or here?

julia> convert(Irrational, 0)
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Irrational
This may have arisen from a call to the constructor Irrational(...),
since type constructors fall back to convert methods.

[malmaud]

Should be pick a default reasonable precision, like Float64, to make complex(pi) work? Or just add a more understandable error message?

[tkelman]

See the last remaining bullet on #21204, cc @giordano

[giordano]

The decision in PR #22928 was to keep the error and don't provide a default behavior. I guess this ticket can be closed, unless someone wants to improve the error message.

[malmaud]

I think this should stay open until the error is approved.

[perrutquist]

complex(pi) is one of many methods that would start working if zero(pi) were defined.

[vtjnash]

We discussed this on triage, and felt that it is better to be explicit about the transforms for irrational numbers into the appropriate computational types and not add more methods to them.

In this way, this type could be viewed as being similar to undef, that exist as a token to pass to various constructors, but is not itself a fully-fledged type (another example of this may be I in LinearAlgebra).