Looping Blocks¶
S++ looping blocks can be either an iteration-based loop or a conditional loop. Both use the loop keyword, but
iteration loops require the in keyword to denote the generator that will be iterated over.
Conditional Loop¶
A conditional loop is the same as a traditional while loop. It requires a boolean condition that is evaluated every
iteration, with an optional else block for if the condition is false on the initial iteration.
loop some_boolean_condition() {
...
}
The optional else block is added to the end of the loop block. The code inside the loop and else blocks will
never both be executed; they are mutually exclusive.
loop some_boolean_condition() {
...
}
else {
...
}
Iteration Loop¶
An iteration loop is syntactic sugar for easier use of generators. The following shows the transformation from an iteration based loop to a boolean loop:
loop i in some_generator() {
...
}
The convention of the iteration variable, in this example i, is determined off of the iterator. The only values that
can be on the right hand side of the in keyword are expressions whose inferred type superimposes the Gen type.
Because of the special check that only 1 Gen type is ever superimposed on a type, the generated type is immediately
inferrable.
For example, the std::vector::Vec[T] type superimposes:
std::iterator::IterMov[T]std::iterator::IterMut[T]std::iterator::IterRef[T]
Each of these types contain method that respectively return (and superimpose):
std::iterator::Iterator[T] -> std::generator::Gen[T]std::iterator::Iterator[&mut T] -> std::generator::Gen[&mut T]std::iterator::Iterator[&T] -> std::generator::Gen[&T]
This allows the selection of the iterator’s convention based on the iteration method chosen. For example, using
loop x in vector.iter_mut() means that x will be the &mut T type.
Note that iteration syntax using loop-in requires the Gen type to use Send=Void, so that the resume method
doesn’t require an argument.
Flow Control¶
See the section on loop flow control statements for more information.