Beyond `if` Statements: Where Else Can a Type with an Explicit `bool` Conversion Be Used Without Casting?

Contextual Conversion to bool Allowed Without a Cast

Your class defines an explicit conversion to bool, enabling you to use its instance 't' directly in conditional statements. However, this explicit conversion poses the question: where else can 't' be used as a bool without a cast?

Contextual Conversion Scenarios

The C standard specifies four main scenarios where a value can be contextually converted to bool:

Statements:

• if, while, for, do-while statements

  <code class="cpp">if (t)
    /* statement */;</code>

Expressions:

• Negation (!), logical AND (&&), logical OR (||), ternary operator (?)

  <code class="cpp">!t
  t &amp;&amp; t2</code>

Compile-Time Tests:

• static_assert, noexcept, explicit, if constexpr (requires constexpr conversion operator)

  <code class="cpp">static_assert(t);
  noexcept(t)</code>

Algorithms and Concepts:

• NullablePointer, predicate or comparator arguments in STL algorithms

  <code class="cpp">NullablePointer T
  std::remove_if(first, last, [&amp;](auto){ return t; });</code>

Additional Notes:

• Narrowing conversions from integers other than 0 and 1 are not permitted in compile-time tests (C 26 onwards).
• Mixing const and non-const conversion operators can lead to confusion.

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