result_ex

#!/bin/bash
#
# Illustrates `Result` to return value and error from a function.

readonly DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
. ${DIR}/../gobash


function sum() {
        # One way to return a value is by passing an "output" argument
        # (an instance of `Result`) to a function, which will be
        # populated in the function.
        local -r res="${1}"
        local -r a="${2}"
        local -r b="${3}"

        # Check all the arguments.
        [ -z "${res}" ] && ctx_w 'No arguments' && return $EC

        # When we detect an error, we write into the default context.
        [ -z "${a}" ] && ctx_w 'a was not set' && return $EC
        [ -z "${b}" ] && ctx_w 'b was not set' && return $EC

        ! is_int "${a}" && ctx_w 'a is not an int' && return $EC
        ! is_int "${b}" && ctx_w 'b is not an int' && return $EC

        # Set the value of the result.
        $res val $(( ${a} + ${b} ))
        return 0
}

ctx_clear
# Not providing any argument.
sum || ctx_show
# Output:
# No arguments
# 18 sum ./result_ex
# 37 main ./result_ex

ctx_clear
# Providing result but no other argument.
res=$(Result)
sum "$res" || ctx_show
# Output:
# a was not set
# 21 sum ./result_ex
# 43 main ./result_ex

ctx_clear
# Providing result and one argument.
res=$(Result)
sum "$res" 5 || ctx_show
# Output:
# b was not set
# 22 sum ./result_ex
# 52 main ./result_ex

ctx_clear
# Providing both arguments but wrong type.
res=$(Result)
sum "$res" "a" "b" || ctx_show
# Output:
# a is not an int
# 24 sum ./result_ex
# 61 main ./result_ex

ctx_clear
# Providing all arguments with correct types.
res=$(Result)
sum "$res" 10 5 || \
        { echo "This should never happen."; }

# Get the value and then print it.
echo $($res val)
# Output: 15

# If there is no error to_string for `Result` print the value.
$res to_string
# Output: 15