Add method map() on Children to wrap easily

[cecton]

Description

Add a function Children::map(&self) to easily wrap children.

Real life example:

use yew::prelude::*;

#[derive(Clone, PartialEq, Properties)]
pub struct ButtonProps {
    #[prop_or_default]
    pub onclick: Callback<MouseEvent>,
    #[prop_or_default]
    pub children: html::Children,
}

#[function_component(Button)]
pub fn button(props: &ButtonProps) -> Html {
    let ButtonProps {
        onclick,
        children,
        // ...
    } = props;

    html! {
        <button
            // ...
            onclick={(!disabled).then_some(onclick.clone())}
        >
            {
                (!children.is_empty())
                    .then(|| html! {
                        <span class="bp3-button-text">
                            {for children.iter()}
                        </span>
                    })
            }
        </button>
    }
}

This can be simplified into:

{
    (children
        .map(|children| html! {
            <span class="bp3-button-text">
                {for children.iter()}
            </span>
        })
}

Checklist

• I have reviewed my own code
• I have added tests

[github-actions]

Visit the preview URL for this PR (updated for commit afcce29):

https://yew-rs-api--pr3039-add-convient-helper-dsruq0op.web.app

_{(expires Tue, 20 Dec 2022 15:39:28 GMT)}

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[github-actions]

Benchmark - SSR

Yew Master

Benchmark	Round	Min (ms)	Max (ms)	Mean (ms)	Standard Deviation
Baseline	10	376.771	391.559	379.649	4.796
Hello World	10	681.386	690.918	683.508	3.026
Function Router	10	2366.675	2383.676	2374.848	5.059
Concurrent Task	10	1007.733	1009.042	1008.461	0.395

Pull Request

Benchmark	Round	Min (ms)	Max (ms)	Mean (ms)	Standard Deviation
Baseline	10	376.776	391.476	381.978	5.052
Hello World	10	734.835	744.337	737.709	3.512
Function Router	10	2405.180	2464.383	2450.333	17.120
Concurrent Task	10	1007.151	1009.236	1008.228	0.689

[github-actions]

Size Comparison

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
async_clock	108.258	108.259	+0.001	+0.001%
boids	172.289	172.295	+0.006	+0.003%
communication_child_to_parent	92.363	92.360	-0.003	-0.003%
communication_grandchild_with_grandparent	106.797	106.799	+0.002	+0.002%
communication_grandparent_to_grandchild	102.658	102.652	-0.006	-0.006%
communication_parent_to_child	89.445	89.444	-0.001	-0.001%
contexts	109.335	109.336	+0.001	+0.001%
counter	87.386	87.385	-0.001	-0.001%
counter_functional	87.802	87.798	-0.004	-0.004%
dyn_create_destroy_apps	90.233	90.234	+0.001	+0.001%
file_upload	101.708	101.706	-0.002	-0.002%
function_memory_game	166.475	166.475	0	0.000%
function_router	350.031	350.035	+0.004	+0.001%
function_todomvc	161.419	161.418	-0.001	-0.001%
futures	226.534	226.535	+0.001	+0.000%
game_of_life	108.142	108.142	0	0.000%
immutable	183.999	183.999	0	0.000%
inner_html	83.808	83.807	-0.001	-0.001%
js_callback	113.015	113.009	-0.006	-0.005%
keyed_list	197.806	197.808	+0.002	+0.001%
mount_point	86.957	86.956	-0.001	-0.001%
nested_list	114.942	114.942	0	0.000%
node_refs	94.876	94.872	-0.004	-0.004%
password_strength	1552.856	1552.857	+0.001	+0.000%
portals	98.146	98.146	0	0.000%
router	320.127	320.122	-0.005	-0.002%
simple_ssr	153.047	153.056	+0.009	+0.006%
ssr_router	394.512	394.511	-0.001	-0.000%
suspense	110.762	110.762	0	0.000%
timer	90.282	90.279	-0.003	-0.003%
todomvc	142.749	142.748	-0.001	-0.001%
two_apps	88.016	88.014	-0.002	-0.002%
web_worker_fib	154.376	154.375	-0.001	-0.001%
webgl	86.532	86.533	+0.001	+0.001%

✅ None of the examples has changed their size significantly.

[hamza1311]

Good addition!

Side note: the example in the PR description is wrong. The closure passed to map should provide children as a parameter

[WorldSEnder]

Looks good to me too! I'm not 100% on board with the name (cause map on an iterator-like thing might mean per-item), but I can't think of a better name, and it's consistent with Option, so 👍 from me.

[cecton]

@WorldSEnder I have the same doubt to be honest but I couldn't find a better name.

There is Option::and_then. But I think it doesn't sound as good as map here.

The actual map on iterator can still be done with children.iter().map(...) (vs children.map(...)).

(I'm merging this for now but I will create another PR if we come up with a better name)