Enhanced 'do' Block Syntax and Error Handling

[gwendal.roue (Gwendal Roué)]

@dmt

Another big difference between do {...} expression and .apply { ... } function with a passed closure is forced Exactly-Once semantic, meaning that the code inside the block is known to be executed once, not relying on implementation of the apply function.

I find this interesting, given a previous attempt at guaranteeing unique closure execution has failed.