what is the idiomatic way of building strings? let...

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[tschuchort]

what is the idiomatic way of building strings? lets says I have an initial string "{ items: " and want to write ints from an array into it to get: `"{ items: 1 2 3 4 5 }". My first idea was something like:

intList.fold("{ items: ") { string, int -> 
    string += "$int "
} += "}"

but it doesnt seem to work