Multiplying strings and integers
Interpreters, Iteration 8
User Story
Your client does want to multiply strings and integers!
User Story #8: Interpreter evaluates a string-integer product.
A Hobbes program can be the multiplication of a string and an integer (in that order).
Examples:
| code | evaluation |
|---|---|
"hi! " * 5 |
"hi! hi! hi! hi! hi! " |
"abc" * 0 |
"" |
456 * "sticks" |
error: not allowed |
"two" * "three" |
error: not allowed |
Of course, this does not invalidate or change integer-integer multiplication.
Your Job
Implement this user story just for your object-oriented interpreter.
Use the same approach that you used for making the addition
operator in the previous iteration. Reuse the
OperatorAlgorithm, but create a new
MultiplicationAlgorithm class.
Do not neglect your refactoring duties. Play around with Extract Method and Rename (especially) to clean up your code and make it more readable. I can't emphasize the name issue too much:
``The first step towards wisdom is calling things by their right names.'' –Chinese proverb
I was very, very wise. The interface for implementing operators
is called "OperatorAlgorithm". The implementation for
addition is called "AdditionAlgorithm". Great
descriptive names!
Make use of Eclipse's Refactor -> Rename! Although, it won't get all of the names in the multiple-dispatch classes. You'll have to change them by hand, but that's what the tests are for: to find the names you have to change!
But I was very, very dumb. Not all operator algorithms want to
"add" expressions together. Calling the method "add()"
is confusing (or will be when you start multiplying with it). So
rename it! Call it something like compute(). In the
context of an "operator algorithm", the idea of "computing" will
make sense. After each renaming, re-run your tests to make sure you
haven't broken anything.
Whenever you come across a name in your code that is vague or an outright lie, change it immediately.