c# - When to use properties instead of functions

Question

This is probably a matter of personal preference, but when do you use properties instead of functions in your code

For instance to get an error log I could say

string GetErrorLog()
{
      return m_ErrorLog;
}

or I could

string ErrorLog
{
     get { return m_ErrorLog; }
}

How do you decide which one to use? I seem to be inconsistent in my usage and I'm looking for a good general rule of thumb. Thanks.

Answer 1

I tend to use properties if the following are true:

• The property will return a single, logic value
• Little or no logic is involved (typically just return a value, or do a small check/return value)

I tend to use methods if the following are true:

• There is going to be significant work involved in returning the value - ie: it'll get fetched from a DB, or something that may take "time"
• There is quite a bit of logic involved, either in getting or setting the value

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In addition, I'd recommend looking at Microsoft's Design Guidelines for Property Usage. They suggest:

Use a property when the member is a logical data member.

Use a method when:

• The operation is a conversion, such as Object.ToString.
• The operation is expensive enough that you want to communicate to the user that they should consider caching the result.
• Obtaining a property value using the get accessor would have an observable side effect.
• Calling the member twice in succession produces different results.
• The order of execution is important. Note that a type's properties should be able to be set and retrieved in any order.
• The member is static but returns a value that can be changed.
• The member returns an array. Properties that return arrays can be very misleading. Usually it is necessary to return a copy of the internal array so that the user cannot change internal state. This, coupled with the fact that a user can easily assume it is an indexed property, leads to inefficient code. In the following code example, each call to the Methods property creates a copy of the array. As a result, 2n+1 copies of the array will be created in the following loop.