Sams Teach Yourself Objective-C in 24 Hours by Jesse Feiler

Author:Jesse Feiler
Language: eng
Format: epub
ISBN: 9780132939874
Publisher: Sams Publishing

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By the Way: Floats, Decimals, and Currencies

Calculations on currencies other than simple addition and subtraction need to take into account the issues involved with rounding fractions. This example does not get into those considerations.

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That is a good start, and it is one that many people would use. This means that the code inside the method practically writes itself:

return units * exchangeRate;

But remember that in Objective-C it is often preferable to use the Objective-C classes rather than raw C types. A better method header might be

– (NSNumber *) convertCurrency: (NSNumber *)units

withRate: (NSNumber *)exchangeRate;

The difference between the first version in which the arguments and return value are all float types and the second in which they are NSNumber objects is that that the latter is more generalized. NSNumber objects can be created from and returned as a multitude of different types. Here are the getters for NSNumber:

• boolValue

• charValue

• decimalValue

• doubleValue

• floatValue

• intValue

• integerValue

• longLongValue

• longValue

• shortValue

• unsignedCharValue

• unsignedIntegerValue

• unsignedIntValue

• unsignedLongLongValue

• unsignedLongValue

• unsignedShortValue

This allows any necessary conversions to happen internally to the NSNumber arguments. You can use and reuse the method. If some types of values are going to be problematic, you can manage them inside the conversion method where they are used.

While you are thinking of generalizing the method, consider the fact that the name is more specific than needed. As implemented at this point, the method works for currency conversion as well as conversions of units of measure. Why limit its usefulness only to currency conversion if it is not necessary? You can always come back later and change the generalized method to a more specific one. Going in the other direction can be a bit more work.

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