Julia add custom message in assert

When working with Julia, it is common to use the assert function to check if certain conditions are met. However, the default error message provided by assert may not always be informative enough. In this article, we will explore three different ways to add a custom message to an assert statement in Julia.

Option 1: Using the `@assert` Macro

One way to add a custom message to an assert statement is by using the @assert macro. This macro allows us to specify a custom message as the second argument. Here’s an example:

@assert x > 0 "x must be greater than 0"

In this example, if the condition x > 0 is not met, the custom message “x must be greater than 0” will be displayed along with the default error message.

Option 2: Using the `assert` Function with a Custom Error Type

Another way to add a custom message to an assert statement is by defining a custom error type and using it with the assert function. Here’s an example:

struct CustomError<T<:AbstractString>> <: Exception
    message::T
end

function assert_custom(condition, message::AbstractString)
    if !condition
        throw(CustomError(message))
    end
end

assert_custom(x > 0, "x must be greater than 0")

In this example, we define a custom error type called CustomError that inherits from Exception. We then define a function called assert_custom that throws an instance of CustomError with the specified message if the condition is not met.

Option 3: Using the `@assert_throws` Macro

The third option is to use the @assert_throws macro, which allows us to check if a specific exception is thrown. We can use this macro to check if a CustomError is thrown with the desired message. Here’s an example:

@assert_throws CustomError "x must be greater than 0" assert_custom(x > 0, "x must be greater than 0")

In this example, the @assert_throws macro checks if the assert_custom function throws a CustomError with the message “x must be greater than 0”. If the condition is not met or the error message is different, the assertion will fail.

After exploring these three options, it is clear that the best option depends on the specific use case. If you simply want to add a custom message to an assert statement, using the @assert macro is the most straightforward approach. However, if you need more control over the error handling, defining a custom error type and using it with the assert function might be a better choice. The @assert_throws macro is useful when you want to check if a specific exception is thrown with a specific message.