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Coding Patterns - objectRegistry

The objectRegistry in OpenFOAM behaves much like a global collection of regIOobject items (and things derived from regIOobject such as IODictionary, IOField, volScalarField, etc). The items within the collection are the so-called registered entries.

The items known by the objectRegistry can either have their storage within the registry or outside of the registry.

• Coding Patterns - objectRegistry
  • Maintaining a cached value

Maintaining a cached value

This is a common use. A derived quantity is calculated within a function object or within a local scope with the following requirements:

1. item should be persistent (available) for other functions
2. reuse or create the item as required.

// Retrieve existing (if any)
auto* fieldPtr = mesh.getObjectPtr<volScalarField>(resultName_);

if (!fieldPtr)
{
    // It does not exist, create a new one. Note use of raw pointer.
    fieldPtr = new volScalarField
    (
        IOobject
        (
            resultName_,
            mesh.time().timeName(),
            mesh.thisDb(),
            IOobject::NO_READ,
            IOobject::NO_WRITE
            // implicit:  IOobject::REGISTER
        ),
        mesh,
        dimensionedScalar(dimless, Zero)
        // implicit:  calculatedType()
    );

    // Pass pointer ownership to the registry
    mesh.objectRegistry::store(fieldPtr);
}

// The field
auto* result = *fieldPtr;

// Perform some calculations...

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