In Julia, you can define a method or function in runtime using the eval function. The eval function evaluates and executes Julia expressions dynamically. Here is an example:
# Define a function that takes two arguments
function add(x, y)
return x + y
end
# Define a new method for the add function
eval("function add(x::String, y::String)\n return parse(Int,x) + parse(Int,y)\nend")
# Call the new method
println(add("3", "5")) # Output: 8
In this example, we defined a add function that takes two arguments. Then, we defined a new method for the add function in runtime using the eval function. The new method takes two strings, converts them into integers using the parse function, and returns the sum. Finally, we called the new method with two strings as arguments, and it returned the expected sum of the two integer values represented by the strings.