[swift-evolution] [Pitch] Extending Swift Literals

[David Sweeris]

The existing literals are both few and pretty foundational to programming, so I don't mind them being slightly "magical". Rather than introducing another dozen "magic" types, wouldn't it be better to allow custom literal types, and have all these types use that system?

- Dave Sweeris

> On Jul 10, 2016, at 22:48, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
> 
> This is purely additive and would not be eligible for Swift 3. 
> gist: https://gist.github.com/erica/c92f6ab115af89d5c4b9161487df6a3c
> 
> -- E
> 
> Extending Swift Literals
> Proposal: TBD
> Author: Erica Sadun
> Status: TBD
> Review manager: TBD
> Introduction
> 
> This proposal expands Swift's language literals to include common cross-platform concepts that need not require.
> 
> Motivation
> 
> A Swift literal represents a fixed value in source code. A literal can be a string, a number (for example an integer), a compound value (such as an array), or one of several predefined "playground" literals including colors, resource file paths, and resource images.
> 
> Swift literals do not have types. They are universal representations that are evaluated and their types inferred from the context in which they are used. Because their nature is typeless, the same color literal can initialize UIColor, NSColor, and SKColor instances. The type cannot be inferred from the source without the context of its destination.
> 
> let color = #colorLiteral(red: 0.8100712299, green: 0.1511939615, blue: 0.4035313427, alpha: 1)
> Detailed Design
> 
> Namespace redesign
> Kind	Literal	Parameters
> Color	`#literal.color(red:, green:, blue:, alpha:)`	floating point values
> Image	`#literal.image(resourceName:)`	String with resource name
> File	`#literal.file(resourceName:)`	String with resource name
> General
> Kind	Literal	Parameters
> Sound	`#literal.audio(resourceName:)`	String with resource name
> URL	`#literal.url(string:)`, `#literal.url(filePath:)`	String with resource location
> Font	`#literal.font(face:, size:)`	string, floating point
> Date	`#literal.date(timeInterval:)`	floating point offset from Unix epoch
> Unicode	`#literal.unicode(name:)`	Official unicode name, e.g. `#literal.unicode(name:"DOG FACE")`
> Geometry
> Kind	Literal	Parameters
> Point	`#literal.point(x:, y:)`, `#literal.point(x:, y:, z:)`, `#literal.point(x:, y:, z:, w:)`	floating point values
> Vector	`#literal.vector(dx:, dy:)`, `#literal.vector(dx:, dy:, dz:)`, `#literal.vector(dx:, dy:, dz:, dw:)`	floating point
> Size	`#literal.size(width:, height:)`, `#literal.size(width:, height:, depth:)` 	floating point
> Rect	`#literal.rect(x:, y:, width:, height:)`	floating point
> Affine Transform	`#literal.affineTransform(a:,b:,c:,d:,tx:,ty:)`, `#literal.affineTransform(translateX:, translateY:)`, `#literal.affineTransform(scaleY:, scaleY:)`, `#literal.affineTransform(rotation:)`, 	floating point
> Bezier Path	`#literal.bezier("M92.21,24.29H75L73,17a8.32,8.32, 0,0,0-8.27-6.74H34.55A7.69,7.69,0,0,0,27,16.6l-2.08 4z")`	String with SVG path notation
> Not included:
> 
> Attributed Strings: I would like to see a way to define attributed strings (using some system like CSS/HTML) but could not think up a simple representation similar to the others mentioned in the preceding table.
> 
> JSON Literals: Again, probably too complex and possibly not worth their weight. If they could exist, they'd have to be imported via a resource or URL and transformed to a local type.
> 
> Impact on Existing Code
> 
> This proposal is purely additive.
> 
> Alternatives Considered
> 
> Using distinct literal names without subsuming them into a namespaced umbrella.
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