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Sep 7, 2017
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circular-buffer: Clarify overwrite #892

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circular-buffer: Clarify the operation of overwrite
Sep 7, 2017
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circular-buffer: Clarify description of test cases for overwrite.
Sep 7, 2017
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8 changes: 4 additions & 4 deletions exercises/circular-buffer/canonical-data.json
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
{
"exercise": "circular-buffer",
"version": "1.0.0",
"version": "1.0.1",
"comments": [
"In general, these circular buffers are expected to be stateful,",
"and each language will operate on them differently.",
Expand All @@ -13,7 +13,7 @@
" If it should succeed, it should produce the item at `expected`. ",
" If it should fail, `expected` will not be present. ",
"write: Writing the item located at `item` should succeed if and only if `should_succeed` is true.",
"overwrite: Write the item located at `item` into the buffer, removing the oldest item if necessary.",
"overwrite: Write the item located at `item` into the buffer, replacing the oldest item if necessary.",
"clear: Clear the buffer.",
"",
"Failure of either `read` or `write` may be indicated in a manner appropriate for your language:",
Expand Down Expand Up @@ -273,7 +273,7 @@
]
},
{
"description": "overwrite removes the oldest item on full buffer",
"description": "overwrite replaces the oldest item on full buffer",
"property": "run",
"capacity": 2,
"operations": [
Expand Down Expand Up @@ -304,7 +304,7 @@
]
},
{
"description": "overwrite doesn't remove an already-read item",
"description": "overwrite replaces the oldest item remaining in buffer following a read",
"property": "run",
"capacity": 3,
"operations": [
Expand Down
19 changes: 13 additions & 6 deletions exercises/circular-buffer/description.md
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Expand Up @@ -29,14 +29,21 @@ If the buffer has 7 elements then it is completely full:
When the buffer is full an error will be raised, alerting the client
that further writes are blocked until a slot becomes free.

The client can opt to overwrite the oldest data with a forced write. In
this case, two more elements — A & B — are added and they overwrite the
3 & 4:
When the buffer is full, the client can opt to overwrite the oldest
data with a forced write. In this case, two more elements — A & B —
are added and they overwrite the 3 & 4:

[6][7][8][9][A][B][5]

Finally, if two elements are now removed then what would be returned is
not 3 & 4 but 5 & 6 because A & B overwrote the 3 & the 4 yielding the
buffer with:
3 & 4 have been replaced by A & B making 5 now the oldest data in the
buffer. Finally, if two elements are removed then what would be
returned is 5 & 6 yielding the buffer:

[ ][7][8][9][A][B][ ]

Because there is space available, if the client again uses overwrite
to store C & D then the space where 5 & 6 were stored previously will
be used not the location of 7 & 8. 7 is still the oldest element and
the buffer is once again full.

[D][7][8][9][A][B][C]