Abstract class constructor in C can't be used in Vala
This is the example https://valadoc.org/camel-1.2/Camel.Sasl.Sasl.html
CamelSasl is an abstract class and camel_sasl_new is just returning a CamelSasl subclass matching the parameters.
When using this function in Vala it stands that it Can't create instance of abstract class 'Camel.Sasl' when this is true, vapigen should probably make abstract classes constructors as static and this binding would then be usable.
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