Muster, diverse
Sammlung interessanter Muster, nicht thematisch geordnet.
Hands in Sight
Inventor's Paradox
Simply Understood Code
Hands in Sight
Name: Hands In View
Problem: The skier fails to commit downhill on steeps and
bumps, resulting in slides, backward falls, and "yard sales".
Context: In order to explore the entire mountain environment,
a skier must be comfortable to any terrain and rapid terrain change. To
take advantage of this pattern the skier should be skiing at a level at
which parallel turns can be linked consistently.
Forces:
Fear of falling is the most basic of all responses
Reliance on equipment is essential
Continuous movement is essential
Fatigue can be a factor in long descents
Commitment downhill over skis is essential for skis to function as
designed
Solution: Concentrate on keeping the hands in view. Bring them
into sight immediately after each pole plant and turn.
Resulting Context: Keeping the hands in view changes the
alignment of the body from sitting timidly back and allowing the edges
to skid out from under the skier. Thus, keeping the hands in view
pulls the body forward and thus downhill, bringing the skier's
weight over the downhill ski, forcing the edge to bite and turn.
Rationale: As steepness increases, the natural tendency of
any sane person is to sit back against the hill and retain the
perpendicularity the inner ear prefers. Unfortunately, skis must be
weighted to perform as designed, the weight causing flex, which in turn
pushes the edges into the snow in an arc, making a turn. Therefore it is
essential to "throw" oneself down the mountain and over the skis,
depending on them to "catch" the fall as they bite into the snow to
turn underneath the perpetually falling skier. Intellectually this can
be clearly understood but fear prevents execution. Concentrating on
something as simple and indirect as "look at your hands" causes the
desired behavior without directly confronting the fear. This is
directly analogous to what occurs when an individual walks: the
weight is thrown forward in a fall, with the consequent forward thrust
of the leg to catch this fall, repeated for left and right sides in a
continuous tension and release of yielding to gravity in order to defy
it.
Author: Don Olson 95/07/07
Originator: Anonymous ski instructor somewhere in Utah.
Wherever you are, thanks for provoding the breakthrough to better
skiing for the author.
Das Muster ist folgendem Buch entnommen:
James O. Coplien: Software Patterns. SIGS 1996.
Inventor's Paradox
Simplify by solving a more general problem. Applied to programming
this means to simplify by writing a more general program.
Split the program into several loosely-coupled building blocks or
aspects. Avoid unnecessary spreading or duplication of information
in program building blocks to improve understandability and to reduce
size of programs. Use appropriate filters to select what is relevant
to one building block from other building blocks.
(This pattern is not about any kind of abstraction mechanism in
programming but it focusses on those abstraction mechanisms
which significantly simplify the solution by solving a much more
general problem.)
Das Muster ist inspiriert durch die Aussage des Mathematikers Georg
Polya: »The more ambitious plan may have more chances of success«
G. Polya, How To Solve It Princeton University Press, 1945
Das Muster stammt von Karl J. Lieberherr College of Computer Science,
Northeastern University Boston
Simply Understood Code
At the lowest levels of a program are chunks of code.
These are the places that need to be understood to
confidently make changes to a program, and ultimately
understanding a program thoroughly requires understanding
these chunks.
In many pieces of code the problem of disorientation is
acute. People have no idea what each component of the code
is for and they experience considerable mental stress as a
result.
Suppose you are writing a chunk of code that is not so
complex that it requires extensive documentation or else
it is not central enough that the
bother of writing such documentation is worth the
effort, especially if the code is clear enough on its
own. How should you approach writing this code?
People need to stare at code in order to understand
it well enough to feel secure making changes to it.
Spending time switching from window to window
or scrolling up and down to see all the relevant
portions of a code fragment takes attention away
from understanding the code and gaining confidence
to modify it.
People can more readily understand things that
they can read it their natural text reading order; for
Western culture this is generally left to right, top
to bottom.
If code cannot be confidently understood, it will
be accidentally broken.
Therefore, Arrange the important parts of the
code so it fits on one page. Make that code understandable
to a person reading it from top to bottom. Do not require
the code to be repeatedly scanned in order to understand
how data is used and how control moves about.
This pattern can be achieved by using the following
patterns: Local Variables Defined and Used on
One Page, which tries to keep local variables on
one page; Assign Variables Once, which tries to
minimize code scanning by having variables
changed just once; Local Variables Reassigned
Above their Uses, which tries to make a variable’s
value apparent before its value is used while scanning from top to
bottom; Make Loops Apparent, which helps people understand parts of a
program that are non-linear while retaining the ability to
scan them linearly; and Use Functions for Loops,
which packages complex loop structure involving
several state variables into chunks, each of which
can be easily understood.
Autor: Peter Gabriel 1995
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