/// <summary>
/// Similar to <see cref="GetOrAddSharedExpression(Type, string, Func{Type, string, Expression}, Type)" />, except this is used when expression
/// builders want to use local variables in block expressions to store the result of some operation in the expression tree built
/// for a particular target. Reusing one local variable is more efficient than declaring the same local multiple times.
/// </summary>
/// <param name="type">The type.</param>
/// <param name="name">The name.</param>
/// <param name="requestingType">Optional - the type of the object requesting this shared expression. If this is provided,
/// then the search for an existing shared expression will only work if the same requesting type was passed previously.</param>
/// <exception cref="InvalidOperationException">Cannot add ParameterExpression: A shared expression of a different type has already been added with the same type and name.</exception>
/// <remarks>When multiple expression trees from multiple targets are brought together into one lambda, there will
/// often be many duplicate variables which could be shared. So, if an <see cref="IExpressionBuilder" /> needs a local variable
/// for a block, instead of simply declaring it directly through the <see cref="Expression.Parameter(Type, string)" /> function,
/// it can use this function instead, which will return a previously created one if available.</remarks>
public ParameterExpression GetOrAddSharedLocal(Type type, string name, Type requestingType = null)
{
// if no sharedExpressions dictionary, then we have a parent which will handle the call for us.
if (this._sharedExpressions == null)
{
return(ParentContext.GetOrAddSharedLocal(type, name, requestingType));
}
try
{
return((ParameterExpression)GetOrAddSharedExpression(type, name, (t, s) => Expression.Parameter(t, s), requestingType));
}
catch (InvalidCastException)
{
throw new InvalidOperationException("Cannot add ParameterExpression: A shared expression of a different type has already been added with the same type and name.");
}
}
