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Coding Patterns - selectors

Coding Patterns - selectors
- Lookups for New() selectors

Lookups for New() selectors

\since 1912

const word modelType(coeffs.get<word>("type"));

auto cstrIter = dictionaryConstructorTablePtr_->cfind(modelType);

if (!cstrIter.found())
{
    FatalIOErrorInLookup
    (
        dict,
        "fvOption",
        modelType,
        *dictionaryConstructorTablePtr_
    ) << exit(FatalIOError);
}

return autoPtr<option>(cstrIter()(name, modelType, coeffs, mesh));

This contains the following aspects:

The dictionary get<word> for retrieval with input checking
The lookup into the HashTable uses cfind() instead of find() to ensure that the const_iterator version will always be used.
The type is auto, since the compiler can correctly deduce the iterator type and we can only make things worse (more typing, wrong information) if we add this ourselves.
Check for the iterator validity using found() or good() methods. Internally these are identical to comparing with an end iterator, but we save typing and potential mismatches by using these dedicated methods.
Exit immediately upon error, leaving the good case to drop through.
Use of the FatalErrorInLookup or FatalIOErrorInLookup macros which wrap standard boilerplate text for the output.

Anti-pattern: The equivalent longhand version (pre-v1912) illustrates the type of repetitive text we avoid:

FatalIOErrorInFunction(dict)
    << "Unknown fvOption type " << modelType
    << "\n\nValid fvOption types :\n"
    << dictionaryConstructorTablePtr_->sortedToc() << nl
    << exit(FatalIOError);