Make json macro pre-allocate capacity for maps #810
Description
Currently an invocation like json!({ "x": 0, "y": 'y' as i8, "z": [] }) expands into:
::serde_json::Value::Object({
let mut object = ::serde_json::Map::new();
let _ = object.insert(...);
let _ = object.insert(...);
let _ = object.insert(...);
object
})It would be better if it were able to allocate capacity up front, such as by:
- let mut object = ::serde_json::Map::new();
+ let mut object = ::serde_json::Map::with_capacity(1 + 1 + 1);