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POWhy C# compiler doesn't call implicit cast operator?
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  1. POWhy C# compiler doesn't call implicit cast operator?
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    copied!<p>Suppose we have following type:</p> <pre><code>struct MyNullable&lt;T&gt; where T : struct { T Value; public bool HasValue; public MyNullable(T value) { this.Value = value; this.HasValue = true; } public static implicit operator T(MyNullable&lt;T&gt; value) { return value.HasValue ? value.Value : default(T); } } </code></pre> <p>And try to compile following code snippet:</p> <pre><code>MyNullable&lt;int&gt; i1 = new MyNullable&lt;int&gt;(1); MyNullable&lt;int&gt; i2 = new MyNullable&lt;int&gt;(2); int i = i1 + i2; </code></pre> <p>This snipped compiled well and without errors. i1 and i2 casts to integer and addition evaluated.</p> <p>But if we have following type:</p> <pre><code>struct Money { double Amount; CurrencyCodes Currency; /*enum CurrencyCode { ... } */ public Money(double amount, CurrencyCodes currency) { Amount = amount; Currency = currency; } public static Money operator + (Money x, Money y) { if (x.Currency != y.Currency) // Suppose we implemented method ConvertTo y = y.ConvertTo(x.Currency); return new Money(x.Amount + y.Amount, x.Currency); } } </code></pre> <p>Try to compile another code snippet:</p> <pre><code>MyNullable&lt;Money&gt; m1 = new MyNullable&lt;Money&gt;(new Money(10, CurrenciesCode.USD)); MyNullable&lt;Money&gt; m2 = new MyNullable&lt;Money&gt;(new Money(20, CurrenciesCode.USD)); Money m3 = m1 + m2; </code></pre> <p>And now the question, why compiler generate "<em>error CS0019: Operator '+' cannot be applied to operands of type 'MyNullable&lt;Money&gt;' and 'MyNullable&lt;Money&gt;'</em>"?</p>
 

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