public/struct-embedding

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      <h2><a href="./">Go by Example မြန်မာဘာသာ</a>: Struct Embedding</h2>
      
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            <p>Go က struct နဲ့ interface တွေကို <em>embedding</em> လုပ်ခြင်းအားဖြင့်
type တွေရဲ့ <em>composition</em> ကို ပိုမိုချောမွေ့စွာ ဖော်ပြနိုင်ပါတယ်။
ဒါကို Go version 1.16+ မှာ မိတ်ဆက်ထားတဲ့ <code>//go:embed</code> directive နဲ့ မတူပါဘူး၊
အဲဒီ directive က file နဲ့ folder တွေကို application binary ထဲ embed လုပ်ဖို့သုံးတာပါ။</p>

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            <a href="https://go.dev/play/p/vlaeBBv3yy4"><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>
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          <pre class="chroma"><span class="kn">import</span> <span class="s">&#34;fmt&#34;</span>
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          <pre class="chroma"><span class="kd">type</span> <span class="nx">base</span> <span class="kd">struct</span> <span class="p">{</span>
    <span class="nx">num</span> <span class="kt">int</span>
<span class="p">}</span>
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          <pre class="chroma"><span class="kd">func</span> <span class="p">(</span><span class="nx">b</span> <span class="nx">base</span><span class="p">)</span> <span class="nf">describe</span><span class="p">()</span> <span class="kt">string</span> <span class="p">{</span>
    <span class="k">return</span> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Sprintf</span><span class="p">(</span><span class="s">&#34;base with num=%v&#34;</span><span class="p">,</span> <span class="nx">b</span><span class="p">.</span><span class="nx">num</span><span class="p">)</span>
<span class="p">}</span>
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            <p><code>container</code> က <code>base</code> ကို <em>embeds</em> လုပ်ထားပါတယ်။ Embedding က
နာမည်မပါတဲ့ field တစ်ခုလိုပုံစံမျိုးပါ။</p>

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<span class="kd">type</span> <span class="nx">container</span> <span class="kd">struct</span> <span class="p">{</span>
    <span class="nx">base</span>
    <span class="nx">str</span> <span class="kt">string</span>
<span class="p">}</span>
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          <pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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            <p>Struct တွေကို literal နဲ့ တည်ဆောက်တဲ့အခါ၊ embedding ကို
တိတိကျကျ initialize လုပ်ပေးရပါတယ်။ ဒီမှာ
embed လုပ်ထားတဲ့ type က field name အဖြစ်သုံးထားပါတယ်။</p>

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    <span class="nx">co</span> <span class="o">:=</span> <span class="nx">container</span><span class="p">{</span>
        <span class="nx">base</span><span class="p">:</span> <span class="nx">base</span><span class="p">{</span>
            <span class="nx">num</span><span class="p">:</span> <span class="mi">1</span><span class="p">,</span>
        <span class="p">},</span>
        <span class="nx">str</span><span class="p">:</span> <span class="s">&#34;some name&#34;</span><span class="p">,</span>
    <span class="p">}</span>
</pre>
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            <p>base ရဲ့ field တွေကို <code>co</code> ကနေ တိုက်ရိုက်သုံးလို့ရပါတယ်။
ဥပမာ <code>co.num</code></p>

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    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Printf</span><span class="p">(</span><span class="s">&#34;co={num: %v, str: %v}\n&#34;</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">num</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">str</span><span class="p">)</span>
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            <p>တခြားနည်းအနေနဲ့ embed လုပ်ထားတဲ့ type နာမည်ကို သုံးပြီး
အပြည့်အစုံရေးလို့ရပါတယ်။</p>

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    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;also num:&#34;</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nx">base</span><span class="p">.</span><span class="nx">num</span><span class="p">)</span>
</pre>
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            <p><code>container</code> က <code>base</code> ကို embed လုပ်ထားတဲ့အတွက်၊ <code>base</code> ရဲ့ method တွေဟာ
<code>container</code> ရဲ့ method တွေလည်း ဖြစ်သွားပါတယ်။ ဒီမှာ <code>base</code> ကနေ
embed လုပ်ထားတဲ့ method ကို <code>co</code> ကနေ တိုက်ရိုက်ခေါ်သုံးထားပါတယ်။</p>

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    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;describe:&#34;</span><span class="p">,</span> <span class="nx">co</span><span class="p">.</span><span class="nf">describe</span><span class="p">())</span>
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          <pre class="chroma">    <span class="kd">type</span> <span class="nx">describer</span> <span class="kd">interface</span> <span class="p">{</span>
        <span class="nf">describe</span><span class="p">()</span> <span class="kt">string</span>
    <span class="p">}</span>
</pre>
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            <p>Method ပါတဲ့ struct တွေကို embed လုပ်ခြင်းအားဖြင့် တခြား struct တွေမှာ
interface implementation တွေ ရရှိနိုင်ပါတယ်။ ဒီမှာ <code>container</code> က
<code>base</code> ကို embed လုပ်ထားတဲ့အတွက် <code>describer</code> interface ကို
implement လုပ်နေတာကို တွေ့ရပါတယ်။</p>

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    <span class="kd">var</span> <span class="nx">d</span> <span class="nx">describer</span> <span class="p">=</span> <span class="nx">co</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">&#34;describer:&#34;</span><span class="p">,</span> <span class="nx">d</span><span class="p">.</span><span class="nf">describe</span><span class="p">())</span>
<span class="p">}</span>
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          <pre class="chroma"><span class="gp">$</span> go run struct-embedding.go
<span class="go">co={num: 1, str: some name}
</span><span class="go">also num: 1
</span><span class="go">describe: base with num=1
</span><span class="go">describer: base with num=1</span></pre>
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        နောက်ဥပမာ: <a href="generics">Generics</a>.
      </p>
      

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      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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