Questions arise while implementing list-ops exercise as library implementation

[glennj]

I’m implementing list-ops as a library, and I've got some questions about the best way to proceed. Consider

source list_ops.sh
double() { echo $(( $1 * 2 ));}
list=( 1 2 3 4 )
list::map double list   # or
list::map double "${list[@]}"

Should the array be passed by name, or should the elements be passed? For a map function it doesn't really matter, but if the list function is something like intersection it would make more sense to pass 2 array names.

Also, struggling with the best way to return a result array:

• the safest way is to force the user to pass an array name:

result=()
list::map double list result    # in some order
printf "%s\n" "${result[@]}"

• the simpler method, command substitution, is subject to word splitting and globbing:

result=( $( list::map double list ) )

[glennj]

For testing, this is what I’ve got in the test script (pending this discussion): run receives an inline bash script.

@test "map non-empty list" {
    [[ $BATS_RUN_SKIPPED == true ]] || skip
    run bash -c '
        source list_ops.sh
        list=(1 3 5 7)
        incr () { echo $(( $1 + 1 )); }
        #result=( $(list::map incr "${list[@]}") )
        result=( $(list::map incr list) )
        echo "${result[*]}"
    '
    [[ $status -eq 0 ]]
    [[ $output == "2 4 6 8" ]]
}

[glennj]

Relates to #373

[glennj]

Just tried another take in the test file:

setup() { source list_ops.sh; }

@test "foo" {
    run bash -c '
        list=(1 3 5 7)
        incr () { echo $(( $1 + 1 )); }
        result=( $(list::map incr list) )
        echo "${result[*]}"
    '
    [[ $status -eq 0 ]]
    [[ $output == "2 4 6 8" ]]
}

The test failed due to the list::map function not existing in the child shell created by run.

This way of writing the tests forces the library to export -f each function.

Is that something a shell library should do?

[IsaacG]

bash sucks at this sort of thing. Consider using known list names. listA listB result. The function is responsible to read from those lists and write to that list.

The only real alternative is to pass variable names all over and use indirection.