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Fixed-width strings: Difference between revisions
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A first implementation used a tree-based approach on top of in-place concatenation. Unfortunately, this resulted in large trees that held references to all right-hand-side strings, and the resulting flatten operation was highly recursive, which is not desirable for small devices. The current approach is a good compromise between low memory usage and a low number of string copy operations. Also, it reduces the number of objects that need to be marked during a GC operation. | A first implementation used a tree-based approach on top of in-place concatenation. Unfortunately, this resulted in large trees that held references to all right-hand-side strings, and the resulting flatten operation was highly recursive, which is not desirable for small devices. The current approach is a good compromise between low memory usage and a low number of string copy operations. Also, it reduces the number of objects that need to be marked during a GC operation. | ||
=== Substrings === | |||
A substring is a dependent string, as above, that holds a reference to its master, the start and the length of the data. A substring of a substring does not reference a dependent string, but rather the master string itself. | |||
Consider the above example: | |||
<table border="1"> | |||
<tr> | |||
<td colspan="4">len=2</td> | |||
<td colspan="4">left=0</td> | |||
</tr> | |||
<tr> | |||
<td>H</td> | |||
<td>i</td> | |||
<td> </td> | |||
<td>w</td> | |||
<td>o</td> | |||
<td>r</td> | |||
<td>l</td> | |||
<td>d</td> | |||
</tr> | |||
</table> | |||
substr (3, 5) would create this dependent string, pointing to "world": | |||
<table border="1"> | |||
<tr> | |||
<td colspan="8">pointer to master</td> | |||
</tr> | |||
<tr> | |||
<td colspan="4">start=3</td> | |||
<td colspan="4">len=5</td> | |||
</tr> | |||
</table> | |||
substr (3, 5).substr (0, 1) would then create this dependent string, where the master still is the original string: | |||
<table border="1"> | |||
<tr> | |||
<td colspan="8">pointer to master</td> | |||
</tr> | |||
<tr> | |||
<td colspan="4">start=3</td> | |||
<td colspan="4">len=1</td> | |||
</tr> | |||
</table> | |||
=== Static string data === | === Static string data === | ||