我尝试使用Rust特性X，要求实施X的任何人都可以转换为X的其他实现。
所以我试图让trait X<T> : From<T> where T: X {}
的声明像这样强制执行：
T但是编译器告诉我它在我的T: X规范中找不到任何类型的参数，因为T: X<...>需要一些类型信息trait X<T, U> : From<T> where T: X<U> {}
。但是这种方式总会有一种类型的论点太少; e.g。
where T: X<_>我能以某种方式解决这个问题吗？不允许<script>
(function ($) {
$.fn.countTo = function (options) {
options = options || {};
return $(this).each(function () {
// set options for current element
var settings = $.extend({}, $.fn.countTo.defaults, {
from: $(this).data('from'),
to: $(this).data('to'),
speed: $(this).data('speed'),
refreshInterval: $(this).data('refresh-interval'),
decimals: $(this).data('decimals')
}, options);
// how many times to update the value, and how much to increment the value on each update
var loops = Math.ceil(settings.speed / settings.refreshInterval),
increment = (settings.to - settings.from) / loops;
// references & variables that will change with each update
var self = this,
$self = $(this),
loopCount = 0,
value = settings.from,
data = $self.data('countTo') || {};
$self.data('countTo', data);
// if an existing interval can be found, clear it first
if (data.interval) {
clearInterval(data.interval);
}
data.interval = setInterval(updateTimer, settings.refreshInterval);
// initialize the element with the starting value
render(value);
function updateTimer() {
value += increment;
loopCount++;
render(value);
if (typeof(settings.onUpdate) == 'function') {
settings.onUpdate.call(self, value);
}
if (loopCount >= loops) {
// remove the interval
$self.removeData('countTo');
clearInterval(data.interval);
value = settings.to;
if (typeof(settings.onComplete) == 'function') {
settings.onComplete.call(self, value);
}
}
}
function render(value) {
var formattedValue = settings.formatter.call(self, value, settings);
$self.html(formattedValue);
}
});
};
$.fn.countTo.defaults = {
from: 0, // the number the element should start at
to: 0, // the number the element should end at
speed: 100, // how long it should take to count between the target numbers
refreshInterval: 100, // how often the element should be updated
decimals: 0, // the number of decimal places to show
formatter: formatter, // handler for formatting the value before rendering
onUpdate: null, // callback method for every time the element is updated
onComplete: null // callback method for when the element finishes updating
};
function formatter(value, settings) {
return value.toFixed(settings.decimals);
}
}(jQuery));
jQuery(function ($) {
// custom formatting example
$('#count-number').data('countToOptions', {
formatter: function (value, options) {
return value.toFixed(options.decimals).replace(/\B(?=(?:\d{3})+(?!\d))/g, ',');
}
});
// start all the timers
$('.timer').each(count);
function count(options) {
var $this = $(this);
options = $.extend({}, options || {}, $this.data('countToOptions') || {});
$this.countTo(options);
}
});
</script>
<div class="wrapper-count">
<div class="counter col_fourth">
<i class="fa fa-code fa-2x"></i>
<h2 class="timer count-title" id="count-number" data-to="140" data-speed="2500"></h2><span><img src="<?php the_field('first_image');?>"></span>
</div>
<div class="counter col_fourth">
<i class="fa fa-coffee fa-2x"></i>
<h2 class="timer count-title" id="count-number" data-to="180" data-speed="2500"></h2><span><img src="<?php the_field('second_image');?>"></span>
</div>
<div class="counter col_fourth">
<i class="fa fa-lightbulb-o fa-2x"></i>
<h2 class="timer count-title" id="count-number" data-to="400" data-speed="2500"></h2><span><img src="<?php the_field('third_image');?>"></span>
</div>
<div class="counter col_fourth end">
<i class="fa fa-bug fa-2x"></i>
<span>£</span><h2 class="timer count-title" id="count-number" data-to="11" data-speed="2500"></h2><span>m</span><span><img src="<?php the_field('fourth_image');?>"></span>
</div>
</div>
<div class="wrapper-count-2">
<div class="counter col_fourth-2">
<p class="count-text-2 ">Startups incubated to date</p>
</div>
<div class="counter col_fourth-2">
<p class="count-text-2 ">Events held annually</p>
</div>
<div class="counter col_fourth-2">
<p class="count-text-2 ">Community of digital and tech entrepreneurs</p>
</div>
<div class="counter col_fourth end-2">
<p class="count-text-2 ">Start-up funding raised so far</p>
</div>
</div>
。
答案 0 :(得分：3)
我认为将实现作为特征的一部分提供更简单，而不是试图限制实施者：
trait Length {
fn unit_in_meters() -> f64;
fn value(&self) -> f64;
fn new(value: f64) -> Self;
fn convert_to<T:Length>(&self) -> T {
T::new(self.value() * Self::unit_in_meters() / T::unit_in_meters())
}
}
struct Mm {
v: f64,
}
impl Length for Mm {
fn unit_in_meters() -> f64 { 0.001 }
fn value(&self) -> f64 { self.v }
fn new(value: f64) -> Mm {
Mm{ v: value }
}
}
struct Inch {
v: f64,
}
impl Length for Inch {
fn unit_in_meters() -> f64 { 0.0254 }
fn value(&self) -> f64 { self.v }
fn new(value: f64) -> Inch {
Inch{ v: value }
}
}
fn main() {
let foot = Inch::new(12f64);
let foot_in_mm: Mm = foot.convert_to();
println!("One foot in mm: {}", foot_in_mm.value());
}
为了好玩，使用associated_consts功能，您可以将方法替换为常量转换因子。
#![feature(associated_consts)]
trait Length {
const UNIT_IN_METERS: f64;
fn value(&self) -> f64;
fn new(value: f64) -> Self;
fn convert_to<T:Length>(&self) -> T {
T::new(self.value() * Self::UNIT_IN_METERS / T::UNIT_IN_METERS)
}
}
struct Mm {
v: f64,
}
impl Length for Mm {
const UNIT_IN_METERS: f64 = 0.001;
fn value(&self) -> f64 { self.v }
fn new(value: f64) -> Mm {
Mm{ v: value }
}
}
struct Inch {
v: f64,
}
impl Length for Inch {
const UNIT_IN_METERS: f64 = 0.0254;
fn value(&self) -> f64 { self.v }
fn new(value: f64) -> Inch {
Inch{ v: value }
}
}
fn main() {
let foot = Inch::new(12f64);
let foot_in_mm: Mm = foot.convert_to();
println!("One foot in mm: {}", foot_in_mm.value());
}