A using statement is a block-style variation of the RAII-style using declaration.

Example

// introducing a binding
using (res = expr) { // evaluate 'expr' and bind to 'res', which is disposed at the end of the block
  ...

} // 'res' is disposed (calls 'res[Symbol.dispose]()')


// multiple bindings
using (res1 = expr1, res2 = expr2) {
    ...
} // res2 is disposed, then res1 is disposed


// no binding
using (void = expr1) { // evaluate 'expr1' and store result in implicit variable

} // implicit variable is disposed

Status

Status: Out of scope

The using statement has been postponed and deemed out of scope for the original proposal. This was cut primarily to reduce the scope of the intial proposal and to focus on the highly preferred RAII-style.

Alternatives

This could also potentially be addressed by the using await declaration.

Postponement Implications

Though the using statement provided a bridge between RAII-style using declarations and the block-style using await statement. Postponing the using statement may decrease the likelihood that the using await statement could advance in a version of ECMAScript that already had using declarations.

History

The initial draft of this proposal used the using statement syntax, as well as the following alternatives, before the proposal settled on the RAII-style using declaration form:

// initial draft
using (const res = expr) { ... }

// Java try-with-resources variant
try (const res = expr) { ... }
try (const res = expr) { ... } finally { }

// other variations
try using (const res = expr) { ... }
try using (const res = expr) { ... } finally { }

// final version
using (res = expr) { ... }

More Information

An early draft of the spec text for using statements can be found in #86.