0001    // The MIT License
0002    //
0003    // Copyright (c) 2015 Gwendal Roué
0004    //
0005    // Permission is hereby granted, free of charge, to any person obtaining a copy
0006    // of this software and associated documentation files (the "Software"), to deal
0007    // in the Software without restriction, including without limitation the rights
0008    // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
0009    // copies of the Software, and to permit persons to whom the Software is
0010    // furnished to do so, subject to the following conditions:
0011    //
0012    // The above copyright notice and this permission notice shall be included in
0013    // all copies or substantial portions of the Software.
0014    //
0015    // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
0016    // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
0017    // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
0018    // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
0019    // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
0020    // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
0021    // THE SOFTWARE.
0022    
0023    let ZipFilter
StandardLibrary.swift:220
    public static let zip = ZipFilter = VariadicFilter { (boxes) in
0024        
0025        // Turn collection arguments into generators. Generators can be iterated
0026        // all together, and this is what we need.
0027        //
0028        // Other kinds of arguments generate an error.
0029        
0030        var zippedGenerators: [AnyGenerator<MustacheBox>] = []
0031        
0032        for box in boxes {
0033            if box.isEmpty {
0034                // Missing collection does not provide anything
0035            } else if let array = box.arrayValue {
0036                // Array
0037                zippedGenerators.append(AnyGenerator(array.generate()))
0038            } else {
0039                // Error
0040                throw MustacheError(kind: .RenderError, message: "Non-enumerable argument in zip filter: `\(box.value)`")
0041            }
0042        }
0043        
0044        
0045        // Build an array of custom render functions
0046        
0047        var renderFunctions: [RenderFunction] = []
0048        
0049        while true {
0050            
0051            // Extract from all generators the boxes that should enter the rendering
0052            // context at each iteration.
0053            //
0054            // Given the [1,2,3], [a,b,c] input collections, those boxes would be
0055            // [1,a] then [2,b] and finally [3,c].
0056            
0057            var zippedBoxes: [MustacheBox] = []
0058            for generator in zippedGenerators {
0059                var generator = generator
0060                if let box = generator.next() {
0061                    zippedBoxes.append(box)
0062                }
0063            }
0064            
0065            
0066            // All generators have been enumerated: stop
0067            
0068            if zippedBoxes.isEmpty {
0069                break;
0070            }
0071            
0072            
0073            // Build a render function which extends the rendering context with
0074            // zipped boxes before rendering the tag.
0075            
0076            let renderFunction: RenderFunction = { (info) -> Rendering in
0077                var context = zippedBoxes.reduce(info.context) { (context, box) in context.extendedContext(box) }
0078                return try info.tag.render(context)
0079            }
0080            
0081            renderFunctions.append(renderFunction)
0082        }
0083        
0084        
0085        // Return a box of those boxed render functions
0086        
0087        return Box(boxable: renderFunctions.map(Box))
0088    }