functional programming - Ambiguous use of functions (Swift 4) -


i've been trying figure out why following code ambiguous...

public func product <t1: sequence, t2: sequence> (_ sequence1: t1, _ sequence2: t2) ->     anysequence<(t1.element, t2.element)> {   return anysequence(     sequence1.flatmap { element1 in       sequence2.map { element2 in         (element1, element2)       }     }   ) }  public func product <t1: lazysequenceprotocol, t2: lazysequenceprotocol> (_ sequence1: t1, _ sequence2: t2) ->     lazysequence<anysequence<(t1.element, t2.element)>> {   return anysequence(     sequence1.flatmap { element1 in       sequence2.map { element2 in         (element1, element2)       }     }   ).lazy }

...when call 2 lazy sequences , call makeiteratorexample.

_ = product([1, 2].lazy, [3, 4].lazy).makeiterator()

yet, following code doesn't have ambiguity...

public struct product2sequence <t1: sequence, t2: sequence>: sequence {   public typealias element = (t1.element, t2.element)   public typealias iterator = anyiterator<element>    private let iterator: iterator    internal init (_ sequence1: t1, _ sequence2: t2) {     self.iterator = anyiterator(       sequence1.flatmap { element1 in         sequence2.map { element2 in           (element1, element2)         }       }.makeiterator()     )   }    public func makeiterator () -> iterator {     return self.iterator   } }  public struct lazyproduct2sequence <t1: lazysequenceprotocol, t2: lazysequenceprotocol>: lazysequenceprotocol {   public typealias element = (t1.element, t2.element)   public typealias iterator = anyiterator<element>    private let iterator: iterator    internal init (_ sequence1: t1, _ sequence2: t2) {     self.iterator = anyiterator(       sequence1.flatmap { element1 in         sequence2.map { element2 in           (element1, element2)         }       }.makeiterator()     )   }    public func makeiterator () -> iterator {     return self.iterator   } }  public func product <t1: sequence, t2: sequence> (_ sequence1: t1, _ sequence2: t2) -> product2sequence<t1, t2> {   return product2sequence(sequence1, sequence2) }  public func product <t1: lazysequenceprotocol, t2: lazysequenceprotocol> (_ sequence1: t1, _ sequence2: t2) ->     lazyproduct2sequence<t1, t2> {   return lazyproduct2sequence(sequence1, sequence2) }

...when call 2 lazy sequences , call makeiteratorexample.

_ = product([1, 2].lazy, [3, 4].lazy).makeiterator()

my reasoning lazy sequence conforms both lazysequenceprotocol , sequence type system doesn't know product choose. definition second version should not work.

i'm using swift 4.0.

what makes second version work?


Comments

Post a Comment

Popular posts from this blog

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m
Read more

javascript - Z-index in d3.js -

i have map , when hover effect on region of map below yellow line , circle, last ones disappear. how can solve problem? http://jsfiddle.net/ot21n9qx/ var arc = g.append("path") .style("fill", "none") .style("stroke", "yellow") .style("stroke-width", 2) .attr("d", "m" + pathorigin[0] + "," + pathorigin[1] + " q" + svgpoint[0] + "," + pathorigin[1] + " " + svgpoint[0] + "," + svgpoint[1]); var circlesize = d3.scale.linear() .domain([0, 0.5, 1]) .range([4, 10, 4]); svg not have z order draws objects in order created. need create path , circle after create highlight regions. here forked fiddle: http://jsfiddle.net/o00fzgaf/1/
Read more