ALib C++ Library
Library Version: 2402 R1
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ElvisOperator Struct Reference


The binary variant of ternary operator "Q ? T : F" is created by leaving out term 'T', which results in "A ? : B". This operator is often called "Elvis Operator" because ?: reminds people to an emoticon of singer Elvis Presley.

Usually the operator chooses 'A' in the case that 'A' can be interpreted as something like not null, not nulled or true in any means. Otherwise it selects 'B'. Due to the type-safe approach of ALib Expressions , the type of 'A' and 'B' must be equal, or at least an auto-cast has to exist that casts the types to a pair of equal types.

This built-in compiler plug-in covers the operator for virtually any type, including custom ones. The implementation invokes box-function FIsTrue on term 'A' and chooses 'A' if the interface returned true, otherwise it chooses 'B'.

Often, the elvis operator is used with strings. Because the default implementation of boxing interface FIsTrue returns true if the boxed value is an array type and the array length is not zero, with strings given (which are arrays of characters) only empty strings evaluate to false. This way the expression:

     "" ?: "Elvis"

rightfully evaluates to string "Elvis".

With this default implementation, it should be very seldom needed to define a custom Elvis-Operator for custom types.

Definition at line 45 of file elvisoperator.hpp.

#include <elvisoperator.hpp>

Inheritance diagram for ElvisOperator:
Collaboration diagram for ElvisOperator:

Public Method Index:

ALIB_API ElvisOperator (Compiler &compiler)
virtual ~ElvisOperator () override
virtual ALIB_API bool TryCompilation (CIBinaryOp &ciBinaryOp) override
- Public Method Index: inherited from CompilerPlugin
 CompilerPlugin (const NString &name, Compiler &compiler)
virtual ~CompilerPlugin ()
virtual bool TryCompilation (CIAutoCast &ciAutoCast)
virtual bool TryCompilation (CIFunction &ciFunction)
virtual bool TryCompilation (CIUnaryOp &ciUnaryOp)

Additional Inherited Members

- Public Field Index: inherited from CompilerPlugin
const NString Name

Constructor(s) / Destructor Details::

◆ ElvisOperator()


compilerThe compiler we will get attached to.

◆ ~ElvisOperator()

virtual ~ElvisOperator ( )

Virtual destructor.

Definition at line 56 of file elvisoperator.hpp.

Method Details:

◆ TryCompilation()

virtual ALIB_API bool TryCompilation ( CIBinaryOp & ciBinaryOp)

Compiles binary elvis operator A ?: B if terms 'A' and 'B' share the same type.

[in,out]ciBinaryOpThe compilation info struct.
true if an entry was found. false otherwise.

Reimplemented from CompilerPlugin.

The documentation for this struct was generated from the following file: