[swift-evolution] Generic Alaises

[James Campbell]

Ross put it better than I ever could :) yes this is what I meant 

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On Wed, Apr 6, 2016 at 1:45 PM -0700, "Ross O'Brien" <narrativium+swift at gmail.com> wrote:










It's not the same topic. Let's take an example: suppose we have a data structure for a graph of nodes and edges, where the nodes and edges are indexed and both have values. So we have a Graph<NodeIndex : Hashable, EdgeIndex : Hashable, NodeValue, EdgeValue>.Now suppose we want a shortest path from one node to another, and we have a data structure to represent that. Now we have a Path<NodeIndex : Hashable, EdgeIndex : Hashable, NodeValue, EdgeValue>. They both have the same 'generic signature'. If you're navigating a Graph<String, Int, City, Motorway>, you're going to want a Path<String, Int, City, Motorway> as output.
Right now you might write that as:func shortestPath<NodeIndex, EdgeIndex, NodeValue, EdgeValue>(graph:Graph<NodeIndex, EdgeIndex, NodeValue, EdgeValue>, startNode: NodeIndex, endNode: NodeIndex> -> Path<NodeIndex, EdgeIndex, NodeValue, EdgeValue>
It might save a fair amount of typing if we had a generic equivalent to both typealias and associatedtype.
associatedgenerics GraphElements = <NodeIndex : Hashable, EdgeIndex : Hashable, NodeValue, EdgeValue>func shortestPath<GraphElements>(graph: Graph<GraphElements>, startNode<GraphElements.NodeIndex>, endNode<GraphElements.NodeIndex>) -> Path<GraphElements>
genericalias NavigationGraphElements = GraphElements<String, Int, City, Motorway>
typealias NavigationGraph = Graph<NavigationGraphElements>// navigationGraph.shortestPath() now returns a Path<NavigationGraphElements>// this last part is closest to the proposal under review.

On Wed, Apr 6, 2016 at 9:05 PM, Milos Rankovic via swift-evolution <swift-evolution at swift.org> wrote:
Chris Lattner has a proposal under review on this topic. 
milos

On 6 Apr 2016, at 20:41, James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
This was inspired from the topic about moving where clauses out of parameter lists.
Certain generics get very long winded, I was wondering if we could create some sort of alias for generics.
func anyCommonElements <T: SequenceType, U: SequenceType where T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element> (lhs: T, _ rhs: U) -> Bool

could be shared across functions like so:
genericalias SequencesWithSameElements<T, U> =  <T: SequenceType, U: SequenceType where T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element>
func anyCommonElements <SequencesWithSameElements> (lhs: T, _ rhs: U) -> Bool
func == <SequencesWithSameElements> (lhs: T, _ rhs: U) -> Bool


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