default-parameters

Default template argument and partial specialization

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The default argument applies to the specialization — and, in fact, a specialization must accept (so to speak) the base template’s default argument(s). Attempting to specify a default in the specialization: template<class A = int, class B=double> class Base {}; template<class B=char> // … …is an error. Likewise, if we change the specialization so that … Read more

How can I avoid issues caused by Python’s early-bound default parameters (e.g. mutable default arguments “remembering” old data)?

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def my_func(working_list=None): if working_list is None: working_list = [] # alternative: # working_list = [] if working_list is None else working_list working_list.append(“a”) print(working_list) The docs say you should use None as the default and explicitly test for it in the body of the function.

C default arguments

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Wow, everybody is such a pessimist around here. The answer is yes. It ain’t trivial: by the end, we’ll have the core function, a supporting struct, a wrapper function, and a macro around the wrapper function. In my work I have a set of macros to automate all this; once you understand the flow it’ll … Read more

Python, default keyword arguments after variable length positional arguments

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It does work, but only in Python 3. See PEP 3102. From glancing over the “what’s new” documents, it seems that there is no 2.x backport, so you’re out of luck. You’ll have to accept any keyword arguments (**kwargs) and manually parse it. You can use d.get(k, default) to either get d[k] or default if … Read more

Does Java support default parameter values?

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No, the structure you found is how Java handles it (that is, with overloading instead of default parameters). For constructors, See Effective Java: Programming Language Guide’s Item 1 tip (Consider static factory methods instead of constructors) if the overloading is getting complicated. For other methods, renaming some cases or using a parameter object can help. … Read more

Set a default parameter value for a JavaScript function

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From ES6/ES2015, default parameters are in the language specification. function read_file(file, delete_after = false) { // Code } just works. Reference: Default Parameters – MDN Default function parameters allow formal parameters to be initialized with default values if no value or undefined is passed. You can also simulate default named parameters via destructuring: // the … Read more

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