Transcript High-Quality Routines

CS242
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Reduce Complexity
Introduce an intermediate, understandable abstraction
Avoid code duplication
Support subclassing
Hide sequences
Hide pointer operations
Improve portability
Simplify complicated boolean tests
Improve performance
Insure all routines are small?
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Isolate complexity
Hide implementation details
Limit effects of changes
Hide global data
Make central points of control
Facilitate reusable code
Accomplish a specific refactoring
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Each routine should do ONE thing and do it
well
Results
Higher reliability
 Easier debugging
 Easier maintainability
 Easier to understand
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Describe everything the routine does
Avoid meaningless, vague or wishy-washy verbs
 Handle, process, output, “deal with”
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Don’t differentiate routine names solely by number –
OutputUser1
Make names of routines as long as necessary (ok, be
reasonable)
To Name a function – describe return value
 sin(), cos(), atan(), etc
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To Name a procedure – strong verb object
 BuildNormalVectorTable(normaltable* normals, raster* r)
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Should be impervious or immune to bad input
(?)
Avoid catch-all routines
Avoid HIDDEN side-effects
Stick to a standard parameter ordering
Limit the number of parameters
Be mindful of the way data is passed to a
routine
Avoid speculative generality
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Solve today’s problem today
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This is true when public
Local, helper, private routines may assume no
bad input
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Use asserts during development
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Catch-alls will have characteristics like flags
that indicate operations to be performed
Dispatch to smaller, simpler functions if you
can’t think of a cleaner design
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Do not modify global data
Do not
Clear memory
 Create anything
 Destroy anything
 Unless that is the purpose of the routine or it is only
for the duration of the routine
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Stick to a standard parameter ordering
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Example:
 Destination first
 Source next
 Flags last
 (any values that modify the destination or source
immediately follow destination or source
 Decreasing order of importance
CopyValue(destRaster, row, column, sourceRaster, row, column);
MapValues(destRaster, WATER, SWAMP);
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Limit the number of parameters to about 7
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Be mindful of the way data is passed to a
routine
Do not pass large structures or strings to be
modified, pass a reference instead
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Solve today’s problem today
 Be general only when you KNOW it will be useful
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This is a potential time sink
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No set rule, except in this class
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We set that arbitrarily at 25 lines
One screen of code: 50–150 lines
Length IS correlated with errors
 Cost?
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Order of parameters:
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Consider your own “in” and “out” keywords
Use a consistent ordering scheme
Use all the parameters
Put status or error variables last
Don’t use routine parameters as working variables
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Input
Modify
Output
Create a local working variable instead
Document interface assumptions about parameters
Limit the number of a routine’s parameters to about seven
Consider an input, modify, output naming convention for parameters
Pass the variables or objects that the routine needs to maintain its
interface
Make sure actual parameters match formal parameters
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Function vs Procedure
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Function returns only one value like sin()
Setting function return values
Check all possible return paths
 Don’t return references or pointers to local data
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Fully parenthesize macro expressions
Surround multiple-statement macros with
curly braces
Name macros like routines so they can be
replaced with routines
Limitations
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Const
Inline
Template
Enum
Typedef
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The documentation provided does not exactly
match the data
But it is sufficient to complete the assignment
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Write routines to accomplish the following in the BMP:
 Read a single value from the BMP
 Set a single value in the BMP
 Fill a row with a value
 Fill a column with a value
 Fill part of a row
 Fill part of a column
 Draw a line segment
 Fill a rectangle
 Fill a non-convex polygon
 Polygon fill - http://alienryderflex.com/polygon_fill/
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Bresenham’s line algorithm
http://en.wikipedia.org/wiki/Bresenham's_li
ne_algorithm
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Cases
All four corners in bounds
 2 corners in bounds
 1 corner in bounds
 No corners in bounds
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