Initialize member variables in a method and not the constructor

I have a public method which uses a variable (only in the scope of the public method) I pass as a parameter we will call A, this method calls a private method multiple times which also requires the parameter.

At present I am passing the parameter every time but it looks weird, is it bad practice to make this member variable of the c开发者_StackOverflow社区lass or would the uncertainty about whether it is initialized out way the advantages of not having to pass it?

Simplified pseudo code:

public_method(parameter a)
    do something with a
    private_method(string_a, a)
    private_method(string_b, a)
    private_method(string_c, a)

private_method(String, parameter a)
    do something with String and a

Additional information: parameter a is a read only map with over 100 entries and in reality I will be calling private_method about 50 times

I had this same problem myself.
I implemented it differently in 3 different contexts to see hands-on what are result using 3 different strategies, see below.

Note that I am type of programmer that makes many changes to the code always trying to improve it. Thus I settle only for the code that is amenable to changes, readbale, would you call this "flexible" code. I settle only for very clear code.

After experimentation, I came to these results:

1. Passing a as parameter is perfectly OK if you have one or two - short number - of such values. Passing in parmeters has very good visibility, clarity, clear passing lines, well visible lifetime (initialization points, destruction points), amenable to changes, easy to track.
   If number of such values begin to grow to >= 5-6 values, I swithc to approach #3 below.

2. Passing values through class members -- did not do good to clarity of my code, eventually I got rid of it. It makes for less clear code. Code becomes muddled. I did not like it. It had no advantages.

3. As alternative to (1) and (2), I adopted Inner class approach, in cases when amount of such values is > 5 (which makes for too long argument list).
   I pack those values into small Inner class and pass such object by reference as argument to all internal members.
   Public function of a class usually creates an object of Inner class (I call is Impl or Ctx or Args) and passes it down to private functions.
   This combines clarity of arg passing with brevity. It's perfect.

Good luck

Edit

Consider preparing array of strings and using a loop rather than writing 50 almost-identical calls. Something like char *strings[] = {...} (C/C++).

This really depends on your use case. Does 'a' represent a state that your application/object care about? Then you might want to make it a member of your object. Evaluate the big picture, think about maintenance, extensibility when designing structures.

If your parameter a is a of a class of your own, you might consider making the private_method a public method for the variable a.

Otherwise, I do not think this looks weird. If you only need a in just 1 function, making it a private variable of your class would be silly (at least to me). However, if you'd need it like 20 times I would do so :P Or even better, just make 'a' an object of your own that has that certain function you need.

A method should ideally not pass more than 7 parameters. Using the number of parameters more than 6-7 usually indicates a problem with the design (do the 7 parameters represent an object of a nested class?).

As for your question, if you want to make the parameter private only for the sake of passing between private methods without the parameter having anything to do with the current state of the object (or some information about the object), then it is not recommended that you do so.

From a performance point of view (memory consumption), reference parameters can be passed around as method parameters without any significant impact on the memory consumption as they are passed by reference rather than by value (i.e. a copy of the data is not created). For small number of parameters that can be grouped together you can use a struct. For example, if the parameters represent x and y coordinates of a point, then pass them in a single Point structure.

Bottomline
Ask yourself this question, does the parameter that you are making as a members represent any information (data) about the object? (data can be state or unique identification information). If the answer to his question is a clear no, then do not include the parameter as a member of the class.

More information

• Limit number of parameters per method?
• Parameter passing in C#