Created
May 3, 2016 06:46
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A riddle (for a code snippet session, maybe)
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// a "generic" function doing some work for us (in this case, just multiply | |
// value with a factor `n`) | |
function times(value, n) { | |
return value * n; | |
} | |
// "higher order function" to generate more specific functions | |
function makeTimes(n) { | |
return function(value) { | |
return times(value, n); | |
} | |
} | |
// using the specific functions (just to demonstrate, all good) | |
const times3 = makeTimes(3); | |
const times7 = makeTimes(7); | |
console.log(times3(3), times7(3)); | |
// we may want to do things "in bulk", i.e. generate multiple higher order | |
// functions "in one go" | |
// This first attempt is broken, why? | |
function makeTimesMultipleBroken(arrayOfNs) { | |
const result = []; | |
for (var i = 0; i < arrayOfNs.length; i++) { | |
result.push(function(value) { | |
return times(value, arrayOfNs[i]); | |
}); | |
} | |
return result; | |
} | |
var someTimes = makeTimesMultipleBroken([ 4, 5 ]); | |
var times4 = someTimes[0], times5 = someTimes[1]; | |
console.log(times4(3), times5(3)); | |
// This second attempt works. Why? | |
function makeTimesMultiple(arrayOfNs) { | |
return arrayOfNs.map(function(n) { | |
return function(value) { | |
return times(value, n); | |
} | |
}); | |
} | |
someTimes = makeTimesMultiple([ 4, 5 ]); | |
times4 = someTimes[0]; | |
times5 = someTimes[1]; | |
console.log(times4(3), times5(3)); |
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