📂Julia

How to Handle Exceptions in Julia

Overview

People who have struggled with severe loneliness know, oh they know

Anyone who has struggled with unknown errors while coding understands the critical importance of errors in programming…

In Julia, errors can be thrown using the error() function or the @error macro. As of Julia v1.63, 25 types of built-in exceptions are defined¹.

Code

julia> log(1 + 2im)
0.8047189562170501 + 1.1071487177940904im

Consider, for instance, when using the logarithmic function $\log$ in a program, only real numbers should be allowed as input. However, Julia essentially provides an extension to complex numbers $\log_{\mathbb{C}}$ by default. The program running without errors is not an accomplishment. Unintended calculations can lead to unexpected problems, so if a calculation we do not want occurs, we should error out and not proceed.

Let’s create a code that restricts the domain of the original log to real numbers $\mathbb{R}$.

error() Function

julia> function Rlog(x)
           if typeof(1 + 2im) <: Real
               return log(x)
           else
               error(DomainError, ": Rlog allow real number only")
           end
       end

       Rlog(1 + 2im)
ERROR: LoadError: DomainError: Rlog allow real number only
Stacktrace:
 [1] error(::Type, ::String)
   @ Base .\error.jl:42
 [2] Rlog(x::Complex{Int64})
   @ Main c:\admin\REPL.jl:7
 [3] top-level scope
   @ c:\admin\REPL.jl:11
in expression starting at c:\admin\REPL.jl:11

In the above Rlog, if the input is not a real number, it is restricted to raise a DomainError.

@error Macro

julia> function Rlog2(x)
           if typeof(1 + 2im) <: Real
               return log(x)
           else
               @error "Rlog2 also allow Real number only"
           end
       end

       Rlog2(1 + 2im)
┌ Error: Rlog2 also allow Real number only
└ @ Main c:\admin\REPL.jl:17

In the above Rlog2, if the input is not a real number, it is limited to throw an error immediately.

Raise and Throw both mean to cause an error to happen, and there’s no significant difference in the big picture. Raise is a term used in Python, etc., while Throw is used in Java, etc.

Full Code

log(1 + 2im)

function Rlog(x)
    if typeof(1 + 2im) <: Real
        return log(x)
    else
        error(DomainError, ": Rlog allow real number only")
    end
end

Rlog(1 + 2im)

function Rlog2(x)
    if typeof(1 + 2im) <: Real
        return log(x)
    else
        @error "Rlog2 also allow Real number only"
    end
end

Rlog2(1 + 2im)

Environment

• OS: Windows
• julia: v1.6.3