can I do something like this with Double Dispatch

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can I do something like this with Double Dispatch

Roelof Wobben
Hello,

Just thinking how to solve the bowling challenge from exercism.

but I wonder if I can do something like this in the method that checks
if I have the right object

I was thinking about this :

Result
-- Strike
-- Spare
-- allOther

then In  Strike something like this

checkForBonus: number1 score2: number2
   ^ number1 + number2 == 10

or am I thinking the totally wrong way to solve this?

Roelof



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Re: can I do something like this with Double Dispatch

Richard O'Keefe
Remember, we cannot see the Smalltalk exercises in exercism.
We cannot help you without knowing what problem you are
trying to solve.  Is this problem basically the same as
or is it different?

Double dispatch is a programming technique,
not an end in itself.

A weird thing about the exercism site is that you can
see *solutions* to problems for a language even if you
cannot see the *problems* themselves.  So I have seen
*solutions* to Bowling in several languages; some with
no objects at all, and some using single dispatch only.
This is a 'medium' problem, meaning the solution is
maybe 2 or 3 pages.

KEEP IT SIMPLE.
Not every *concept* needs to be a *class*.


On Sat, 6 Apr 2019 at 21:53, Roelof Wobben <[hidden email]> wrote:
Hello,

Just thinking how to solve the bowling challenge from exercism.

but I wonder if I can do something like this in the method that checks
if I have the right object

I was thinking about this :

Result
-- Strike
-- Spare
-- allOther

then In  Strike something like this

checkForBonus: number1 score2: number2
   ^ number1 + number2 == 10

or am I thinking the totally wrong way to solve this?

Roelof



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Re: can I do something like this with Double Dispatch

Roelof Wobben
it is almost the same.

here exercism challenge looks like this :

Scoring Bowling

The game consists of 10 frames. A frame is composed of one or two ball throws with 10 pins standing at frame initialization. There are three cases for the tabulation of a frame.

  • An open frame is where a score of less than 10 is recorded for the frame. In this case the score for the frame is the number of pins knocked down.

  • A spare is where all ten pins are knocked down by the second throw. The total value of a spare is 10 plus the number of pins knocked down in their next throw.

  • A strike is where all ten pins are knocked down by the first throw. The total value of a strike is 10 plus the number of pins knocked down in the next two throws. If a strike is immediately followed by a second strike, then the value of the first strike cannot be determined until the ball is thrown one more time.

Here is a three frame example:

Frame 1 Frame 2 Frame 3
X (strike) 5/ (spare) 9 0 (open frame)

Frame 1 is (10 + 5 + 5) = 20

Frame 2 is (5 + 5 + 9) = 19

Frame 3 is (9 + 0) = 9

This means the current running total is 48.

The tenth frame in the game is a special case. If someone throws a strike or a spare then they get a fill ball. Fill balls exist to calculate the total of the 10th frame. Scoring a strike or spare on the fill ball does not give the player more fill balls. The total value of the 10th frame is the total number of pins knocked down.

For a tenth frame of X1/ (strike and a spare), the total value is 20.

For a tenth frame of XXX (three strikes), the total value is 30.

Requirements

Write code to keep track of the score of a game of bowling. It should support two operations:

  • roll(pins : int) is called each time the player rolls a ball. The argument is the number of pins knocked down.
  • score() : int is called only at the very end of the game. It returns the total score for that game.

and the input is like this : 

test05_ConsecutiveSparesEachGetAOneRollBonus
    | result |
    result := bowlingCalculator
        scoreAfterRolling: #(5 5 3 7 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0).
    self assert: result equals: 31

Roelof




Op 8-4-2019 om 11:43 schreef Richard O'Keefe:
Remember, we cannot see the Smalltalk exercises in exercism.
We cannot help you without knowing what problem you are
trying to solve.  Is this problem basically the same as
or is it different?

Double dispatch is a programming technique,
not an end in itself.

A weird thing about the exercism site is that you can
see *solutions* to problems for a language even if you
cannot see the *problems* themselves.  So I have seen
*solutions* to Bowling in several languages; some with
no objects at all, and some using single dispatch only.
This is a 'medium' problem, meaning the solution is
maybe 2 or 3 pages.

KEEP IT SIMPLE.
Not every *concept* needs to be a *class*.


On Sat, 6 Apr 2019 at 21:53, Roelof Wobben <[hidden email]> wrote:
Hello,

Just thinking how to solve the bowling challenge from exercism.

but I wonder if I can do something like this in the method that checks
if I have the right object

I was thinking about this :

Result
-- Strike
-- Spare
-- allOther

then In  Strike something like this

checkForBonus: number1 score2: number2
   ^ number1 + number2 == 10

or am I thinking the totally wrong way to solve this?

Roelof