[swift-evolution] For loop

Ted F.A. van Gaalen tedvgiosdev at gmail.com
Mon Mar 7 18:48:57 CST 2016

Apart from the indirect .stride method, (which is good for collections)
there are still no adequate equivalents for   
 as used often in ‘traditional’ programming
for floating point numbers. 

Of course, one can also code this in a “while {}”
but this would be cumbersome.

Because of this I am currently replacing for;;
by a global function ‘iterate’ :

/// Tested in Xcode Version 7.2.1 (7C1002) - Playground
// perhaps it should have generic parameters..
// and also a variant with floating point tolerance

func iterate(from from: Double,
                    to: Double,
                    by: Double,
                 block: (v: Double) -> Void)
    let low:  Double
    let high: Double
    let moveForward: Bool

    var current = from
    if from < to
        low  = from
        high = to
        moveForward = true
        low  = to
        high = from
        moveForward = false
    var iterator = 0

    while current >= low  &&
          current <= high
        block(v: current)  // <<<<<<<<<<<<<<<<<<
        iterator += 1        // imho  iterator++   looks a lot cleaner 
        if moveForward
            current = low + Double(iterator) * by
            current = high - Double(iterator) * by

////// Usage of the above function e.g.: /////////////

var factor = 5.0

iterate(from: 0.0, to: -2.0, by: 0.01,  block:
        (v: Double) in
        print("v = \(v) v * factor \(v * factor)")


This tiny simple function is very efficient.
I did not yet run benchmarks on it,
but it probably is a lot faster than fetching values
from a pseudo-collection as with .stride.

Still, imho a better option would be as a Swift
language element:

for v from v1 to v2 by vstep {}

I will then write a proposal for it, unless
someone has a better solution?

All this would not have been necessary if the
for ;;   was not killed.

Kind Regards


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