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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example မြန်မာဘာသာ: Generics</title>
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<div class="example" id="generics">
<h2><a href="./">Go by Example မြန်မာဘာသာ</a>: Generics</h2>
<table>
<tr>
<td class="docs">
<p>Version 1.18 ကစပြီး Go မှာ <em>generics</em> (သို့) <em>type parameters</em> လို့လည်းခေါ်တဲ့
feature ကိုထည့်သွင်း support လုပ်ထားပါတယ်။</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://go.dev/play/p/IQhCPyH1pP3"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
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<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
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<td class="docs">
<p>Generic function ရဲ့ ဥပမာအနေနဲ့၊ <code>MapKeys</code> က map ရဲ့ဘယ်လို type မျိုးကိုမဆို လက်ခံပြီး
သူ့ရဲ့ key တွေကို slice အဖြစ် ပြန်ပေးပါတယ်။
ဒီ function မှာ type parameter နှစ်ခုရှိပါတယ် - <code>K</code> နဲ့ <code>V</code>။
<code>K</code> မှာ <code>comparable</code> ဆိုတဲ့ <em>constraint</em> ရှိပါတယ်၊ ဆိုလိုတာက
ဒီ type ရဲ့ တန်ဖိုးတွေကို <code>==</code> နဲ့ <code>!=</code> operator တွေနဲ့ နှိုင်းယှဉ်လို့ရပါတယ်။
ဒါက Go မှာ map key တွေအတွက် လိုအပ်ချက်တစ်ခုဖြစ်ပါတယ်။
<code>V</code> မှာတော့ <code>any</code> constraint ရှိပါတယ်၊ ဆိုလိုတာက သူ့ကို ဘာမှ ကန့်သတ်မထားဘူးဆိုတာပါ
(<code>any</code> က <code>interface{}</code> ရဲ့ alias ဖြစ်ပါတယ်)။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nx">MapKeys</span><span class="p">[</span><span class="nx">K</span> <span class="nx">comparable</span><span class="p">,</span> <span class="nx">V</span> <span class="nx">any</span><span class="p">](</span><span class="nx">m</span> <span class="kd">map</span><span class="p">[</span><span class="nx">K</span><span class="p">]</span><span class="nx">V</span><span class="p">)</span> <span class="p">[]</span><span class="nx">K</span> <span class="p">{</span>
<span class="nx">r</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="nx">K</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
<span class="k">for</span> <span class="nx">k</span> <span class="o">:=</span> <span class="k">range</span> <span class="nx">m</span> <span class="p">{</span>
<span class="nx">r</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">r</span><span class="p">,</span> <span class="nx">k</span><span class="p">)</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">r</span>
<span class="p">}</span>
</pre>
</td>
</tr>
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<td class="docs">
<p>Generic type ရဲ့ ဥပမာအနေနဲ့၊ <code>List</code> ရဲ့ values တွေက any type ဖြစ်တဲ့
singly-linked list တစ်ခုဖြစ်ပါတယ်။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">type</span> <span class="nx">List</span><span class="p">[</span><span class="nx">T</span> <span class="nx">any</span><span class="p">]</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">head</span><span class="p">,</span> <span class="nx">tail</span> <span class="o">*</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]</span>
<span class="p">}</span>
</pre>
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<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">type</span> <span class="nx">element</span><span class="p">[</span><span class="nx">T</span> <span class="nx">any</span><span class="p">]</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">next</span> <span class="o">*</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]</span>
<span class="nx">val</span> <span class="nx">T</span>
<span class="p">}</span>
</pre>
</td>
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<td class="docs">
<p>ပုံမှန် type တွေမှာလိုပဲ generic type တွေမှာလည်း method တွေ သတ်မှတ်လို့ရပါတယ်၊
ဒါပေမယ့် type parameter တွေကို ထည့်ထားဖို့လိုပါတယ်။ Type က <code>List[T]</code> ဖြစ်ပြီး <code>List</code> မဟုတ်ပါဘူး။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="p">(</span><span class="nx">lst</span> <span class="o">*</span><span class="nx">List</span><span class="p">[</span><span class="nx">T</span><span class="p">])</span> <span class="nf">Push</span><span class="p">(</span><span class="nx">v</span> <span class="nx">T</span><span class="p">)</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="o">==</span> <span class="kc">nil</span> <span class="p">{</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">head</span> <span class="p">=</span> <span class="o">&</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]{</span><span class="nx">val</span><span class="p">:</span> <span class="nx">v</span><span class="p">}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="p">=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">head</span>
<span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span><span class="p">.</span><span class="nx">next</span> <span class="p">=</span> <span class="o">&</span><span class="nx">element</span><span class="p">[</span><span class="nx">T</span><span class="p">]{</span><span class="nx">val</span><span class="p">:</span> <span class="nx">v</span><span class="p">}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span> <span class="p">=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">tail</span><span class="p">.</span><span class="nx">next</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
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<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="p">(</span><span class="nx">lst</span> <span class="o">*</span><span class="nx">List</span><span class="p">[</span><span class="nx">T</span><span class="p">])</span> <span class="nf">GetAll</span><span class="p">()</span> <span class="p">[]</span><span class="nx">T</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">elems</span> <span class="p">[]</span><span class="nx">T</span>
<span class="k">for</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">lst</span><span class="p">.</span><span class="nx">head</span><span class="p">;</span> <span class="nx">e</span> <span class="o">!=</span> <span class="kc">nil</span><span class="p">;</span> <span class="nx">e</span> <span class="p">=</span> <span class="nx">e</span><span class="p">.</span><span class="nx">next</span> <span class="p">{</span>
<span class="nx">elems</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">elems</span><span class="p">,</span> <span class="nx">e</span><span class="p">.</span><span class="nx">val</span><span class="p">)</span>
<span class="p">}</span>
<span class="k">return</span> <span class="nx">elems</span>
<span class="p">}</span>
</pre>
</td>
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<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
<span class="kd">var</span> <span class="nx">m</span> <span class="p">=</span> <span class="kd">map</span><span class="p">[</span><span class="kt">int</span><span class="p">]</span><span class="kt">string</span><span class="p">{</span><span class="mi">1</span><span class="p">:</span> <span class="s">"2"</span><span class="p">,</span> <span class="mi">2</span><span class="p">:</span> <span class="s">"4"</span><span class="p">,</span> <span class="mi">4</span><span class="p">:</span> <span class="s">"8"</span><span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Generic function တွေကို ခေါ်သုံးတဲ့အခါ၊ <em>type inference</em> ကို အားကိုးနိုင်ပါတယ်။
<code>MapKeys</code> ကို ခေါ်တဲ့အခါ <code>K</code> နဲ့ <code>V</code> အတွက် type တွေကို သတ်မှတ်ပေးစရာမလိုတာကို သတိထားပါ -
compiler က သူ့ဘာသာ အလိုအလျောက် ခန့်မှန်းပေးပါတယ်။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"keys:"</span><span class="p">,</span> <span class="nf">MapKeys</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>… ဒါပေမယ့် လိုချင်ရင်တော့ တိတိကျကျ သတ်မှတ်ပေးလို့လည်း ရပါတယ်။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">_</span> <span class="p">=</span> <span class="nx">MapKeys</span><span class="p">[</span><span class="kt">int</span><span class="p">,</span> <span class="kt">string</span><span class="p">](</span><span class="nx">m</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"> <span class="nx">lst</span> <span class="o">:=</span> <span class="nx">List</span><span class="p">[</span><span class="kt">int</span><span class="p">]{}</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">10</span><span class="p">)</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">13</span><span class="p">)</span>
<span class="nx">lst</span><span class="p">.</span><span class="nf">Push</span><span class="p">(</span><span class="mi">23</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"list:"</span><span class="p">,</span> <span class="nx">lst</span><span class="p">.</span><span class="nf">GetAll</span><span class="p">())</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="gp">$</span> go run generics.go
<span class="go">keys: [4 1 2]
</span><span class="go">list: [10 13 23]</span></pre>
</td>
</tr>
</table>
<p class="next">
နောက်ဥပမာ: <a href="errors">Errors</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> နှင့် <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</div>
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