#swift-lang

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Working at being lazy

As teased in the previous article, suppose you want a new kind of lazy evaluation. You want to be able to generate a lazy sequence that represents the first n values of a container.

Here’s how you could add it to LazyRandomAccess:

extension LazyRandomAccessCollection { func first_n (n: LazyRandomAccessCollection.IndexType.DistanceType) -> LazySequence< PermutationGenerator<…

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Changes in the Swift Standard Library in Beta 4

Other than access control,1 no big changes to the language with Beta 4, unlike with Beta 3. But still plenty of changes to the standard library.

Some small bits and pieces:

Float and Double are no longer random access indices. Who was planning on indexing a collection with a Double, anyway? Just how big was your collection going to be?2

uppercaseString and lowercaseStringproperties are gone…

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Jumping to conclusions

In an article yesterday, I mentioned that I wasn’t having much luck extending Dictionary to give it an initializer that took a sequence of tuples, because my attempt wasn’t compiling, even though I was sure that it should:

extension Dictionary { init (_ seq: S) { self.init() for (k,v) in seq { self[k] = v } } }

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On dictionaries and initializers, in which I give up and use a for loop

On Dictionaries and initializers, in which I give up and use a for loop.

On twitter, @rob_rix confessed that he’d given up and used a for loop. @rbrockerhoff replied he had too, in his case because you can’t create a dictionary from an array.

That tweet sent me deep down the rabbit hole experimenting with Dictionary. I keep wanting to fix it, like a scruffy boyfriend. But like with said boyfriend, that’s easier said than done.

Warning: some of the below is very…

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Swift Structs and accessing properties by name

Brent Simmons posted a blog article today about a feature he was missing from Swift that was readily available in Objective-C – the ability to access properties of an object indirectly using a string.

Brent’s goal is to be able to write some generic code that compares various different properties. Here’s how he puts it:1

For every merge-able property there are really two properties, and there’s…

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Always write a general version

Always write a general version of your higher-order function in #swiftlang

Suppose you want to find the minimum value in an array. Well, the Swift standard library has you covered:

let a = [6, 2, 4, 7, 8, 10] minElement(a) // returns 2

Ok that’s cool. But suppose you have an array of strings of integers and you want the minimum numeric value.

Well, I guess you could map them to Int and then use the same function:

let a = ["6", "2", "4", "7", "8", "10"] minElement(…

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Swift's Lazy Collections and Sequences

Swift’s Lazy Collections and Sequences

The Swift non-member function map acts much like the Array.map member function, except you can pass in any kind of sequence or collection (click here for an article on how to write an algorithm like this).

But if you look at what map returns, it isn’t an array of results. It’s an object (a MapColectionView or a MapSequenceView).

That’s because map evaluates its results lazily. When you call map

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Adding different types of number using multiple dispatch

Adding different types of number using multiple dispatch

This is part of a series on solving Paul Graham’s accumulator problem in Swift. You can find Part 1 here.

In the previous post, we solved the requirement that our accumulator accept any kind of numeric type, and to “upgrade” the type it returns from an integer to floating point only the first time it is called with a floating point number, using the Swift Any type:

func foo(var n: Any) -> (Any)…

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