[feature request] add associative array support to mapfile

[Léa Gris]

Here is a Bash model of how, associative array support could be added to 
mapfile, replacing the need for interpreted while-loop read and logic by 
a much more efficient improved mapfile built-in:

> #!/usr/bin/env bash
>
> kv_cr_stream () {
>   printf 'key1=value1\nkey2=value=2\nkey 3=value3\n'
> }
>  
> kv_null_stream () {
>   printf 'key1=value1\0key2=value=2\0key\n3=value3\0'
> }
>
> declare -A assoc_cr=()
>
> # Load associative array from line records
> # Proposed new feature:
> # IFS='=' mapfile -A assoc_cr
> while IFS='=' read -r k v || [[ -n $k && -n $v ]]; do
>   assoc_cr[$k]=$v
> done < <(kv_cr_stream)
>
> declare -p assoc_cr
>
> declare -A assoc_null=()
>
> # Load associative array from null delimited records
> # Proposed new feature:
> # IFS='=' mapfile -d '' -A assoc_null
> while IFS='=' read -r -d '' k v || [[ -n $k && -n $v ]]; do
>   assoc_null[$k]=$v
> done < <(kv_null_stream)
>
> declare -p assoc_null

Expected output:
> declare -A assoc_cr=([key2]="value=2" [key1]="value1" ["key 3"]="value3" )
> declare -A assoc_null=([key2]="value=2" [key1]="value1" [$'key\n3']="value3" )




--
Léa Gris