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Workaround for Delphi 2010 compiler error “E2076 This form of method call only allowed for class methods” when it infers a generic parameter type.

Posted by jpluimers on 2015/09/10

Generic support in Delphi took a very long time to get stabilised. Which means that compilers older than Delphi XE2 are hardly usable for code using generics. XE did get better, but Delphi 2010 and especially Delphi 2009 were hopeless.

A while ago, I bumped into another subtle error “E2076 This form of method call only allowed for class methods” when back-porting to Delphi 2010 the code like below calling the Spring4D unit Spring.SystemUtils which has a TEnum class that includes this TEnum.GetName<T> method:

    class function GetName<T>(const value: T): string; overload; static;

In Delphi XE and up, you do not have to specify the generic parameter T: the compiler automatically infers it.

In Delphi 2010, you have to, otherwise you will get the (totally unrelated!) error “E2076 This form of method call only allowed for class methods“.

Example code:

procedure Test;
RuntimeError: TRuntimeError;
Name: string;
RuntimeError := reNone;
// in the Spring.SystemUtils unit:
// class function TEnum.GetName<T>(const value: T): string;
// Workaround in Delphi 2010 (also works in Delphi XE+, but these do not require the Generic type to be specified).
Name := TEnum.GetName<TRuntimeError>(RuntimeError);
// Delphi 2010 does infer the type of the generic parameter, but then barfs with error E2076.
// Delphi XE+ infers the parameter type and do not generate an error: no need to explicitly specify the generic type:
Name := TEnum.GetName(RuntimeError); // Delphi 2010: [DCC Error] : E2076 This form of method call only allowed for class methods


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