# Crashed Julia with <

Hi,

I have defined the following two types:

``````struct Percentage <: Real
value::Float64
Percentage(x) = x < 0 ? new(0) : x > 1 ? new(1) : new(round(x, digits = 6))
end

Base.show(io::IO, x::Percentage) = print(io, "\$(x.value * 100)%")

Base.convert(::Type{Percentage}, x::Real) = Percentage(x)
Base.convert(::Type{Percentage}, x::Percentage) = x

Base.promote_rule(::Type{T}, ::Type{Percentage}) where T <: Real = Percentage

import Base: +, -, <, >, <=, >=, ==

+(x::Percentage, y::Percentage) = Percentage(x.value + y.value)
-(x::Percentage) = Percentage(-x.value)
-(x::Percentage, y::Percentage) = Percentage(x.value - y.value)
<(x::Percentage, y::Percentage) = x.value < y.value
<=(x::Percentage, y::Percentage) = x.value <= y.value
>(x::Percentage, y::Percentage) = x.value > y.value
>=(x::Percentage, y::Percentage) = x.value >= y.value
==(x::Percentage, y::Percentage) = x.value == y.value

Base.max(x::Percentage, y::Percentage) = Percentage(max(x.value, y.value))
Base.min(x::Percentage, y::Percentage) = Percentage(min(x.value, y.value))

mutable struct Health <: Real
current::Percentage
Health(current=1) = new(current)
end

Base.convert(::Type{Health}, x::Real) = Health(x)
Base.convert(::Type{Health}, x::Health) = x

Base.promote_rule(::Type{T}, ::Type{Health}) where T <: Real = Health

import Base: +, -, <, >, <=, >=, ==

+(x::Health, y::Health) = Health(x.current + y.current)
-(x::Health) = Health(-x.current)
-(x::Health, y::Health) = Health(x.current - y.current)
<(x::Health, y::Health) = x.current < y.current
<=(x::Health, y::Health) = x.current <= y.current
>(x::Health, y::Health) = x.current > y.current
>=(x::Health, y::Health) = x.current >= y.current
==(x::Health, y::Health) = x.current == y.current

Base.max(x::Health, y::Health) = Health(max(x.current, y.current))
Base.min(x::Health, y::Health) = Health(min(x.current, y.current))
``````

When I type

``````Health(0.1) < Percentage(0.2)
``````

in the REPL, I get the message that Julia has exited.

Iām using JuliaPro 1.5.2-2 on Mac OS X 10.15.7

Is there anyone who has an idea what is going on?

Stef

You have specified that `Health` and `Percentage` take precedence over other `Real` types but have not specified which of them takes precedence. As both are subtypes of `Real` themselves, that triggers an error.

On Linux, I get stack overflow from promotions.

In short, you need `promote_rule(::Type{Percentage}, ::Type{Health})`.

3 Likes

Apparently I needed to reverse the order of the types to solve it.

``````promote_rule(::Type{Health}, ::Type{Percentage})
``````