I recently ran into an issue overriding `zero`

for my own `Number`

:

```
julia> immutable Infinity <: Number end
julia> Base.zero(::Infinity) = 0
julia> import Base: +
julia> +(::Infinity,::Int) = Infinity()
+ (generic function with 181 methods)
julia> reduce(+,[Infinity(),Infinity()])
ERROR: MethodError: Cannot `convert` an object of type Int64 to an object of type Infinity
This may have arisen from a call to the constructor Infinity(...),
since type constructors fall back to convert methods.
Stacktrace:
[1] _mapreduce(::Base.#identity, ::Base.#+, ::IndexLinear, ::Array{Infinity,1}) at ./reduce.jl:260
[2] reduce(::Function, ::Array{Infinity,1}) at ./reduce.jl:321
```

The issue appears to be that `zero{T<:Number}(::T)`

is expected to return a `T`

.

Is this a bug, or is this part of the `Number`

“Interface”? Is the `Number`

“Interface” written down anywhere?