PITCHME.md

Named Parameters

Seeking Stage 1

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Overview

Use Cases

Areas of Investigation

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Overview

+++

An opt-in mechanism to expose named parameters.

// ... whe you write this ...
function dostuff(b as b, c as c) {
}

// ... you enable callers like this ...
dostuff(b: 1, c: false); 

@[1-4] (You use "as" to expose named parameters ...) @[5-6] (... so your callers can use them ...)

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Use Cases

+++

Long parameters list

// Signature:
// Date.UTC(year, month[, day[, hour[, minute[, second[, millisecond]]]]])

// ... without named parameters ...
var utcDate = new Date(Date.UTC(96, 11, 1, 0, 0, 0));

// ... with named parameters ...
var utcDate = new Date(Date.UTC(
  year: 96, 
  month: 11, 
  day: 1, 
  hour: 0, 
  minute: 0, 
  millisecond: 0
));

@[1-2] @[4-5] @[7-15]

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WebGL

// ... what does this mean? ...
ctx.drawImage(image, 33, 71, 104, 124, 21, 20, 87, 104);

// ... ah, much clearer ...
ctx.drawImage(
  image: image,
  sx: 33,
  sy: 71,
  swidth: 104,
  sHeight: 124,
  dx: 21,
  dy: 20,
  dWidth: 87,
  dHeight: 104
);

@[1-2] @[4-15]

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Uncommon parameters

// ...  is it bubble or capture? ...
el.addEventListener("mouseup", listener, true)

// ... ah, ok, capturing ...
el.addEventListener("mouseup", listener, capture: true)

@[1-2] @[3-5]

+++

Parameters of the same type

// as opposed to move(100, 200) is the 100 x or y?
move(x: 100, y: 200);

// as opposed to resize(20, 30) is 20 the width or height?
resize(width: 20, height: 30); 

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Multiple optional parameters

// Signature:
blob.slice([start [, end [, contentType]]]);

// Awkward way to change the mime type:
let blob = source.slice(
  undefined, undefined, "image/jpeg");

// Error-prone way to change the mime type:
let blob = source.slice(
  0, source.size, "image/jpeg");

// With named parameters:
let blob = source.slice(contentType: "image/jpeg")

@[1-2] @[4-6] @[8-10] @[12-13]

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Areas of Investigation

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mixed parameters

// Can we intermingle named parameters with positional?
fetch("url.json", option: {
  ...
});

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Stage 1?