4 ms·

Ok I give you this one, but I still don't think that minimizing the size of a length field using a flexible width encoding is a good idea except when talking ab

Ok I give you this one, but I still don't think that minimizing the size of a length field using a flexible width encoding is a good idea except when talking about extremely specialized string encodings (like compression schemes). Flexible width encoding is more complicated compared to simple member access to get at the first character. And how do you handle construction of a string whose size you don't know yet? You might have to move the string away to make space for a bigger string length field. I don't like it.

thaumasiotes 4y ago
> Flexible width encoding is more complicated compared to simple member access to get at the first character. I don't think this is true either. It's almost true. But what happens if the string length is 0? If you make the assumption that you can access the first character of a zero-length string by just grabbing whatever is in memory after the string header, you're going to make the exact mistake the length field is there to stop you from making, a memory access violation. You have to process the length field in order to do any access at all; many strings don't have a first character. > And how do you handle construction of a string whose size you don't know yet? You might have to move the string away to make space for a bigger string length field. That's true; you'll either need to be willing to store the character data and the length metadata in separate locations, or you'll need to be willing to occasionally move the data around.
- jstimpfle 4y ago
  Obviously I mean get at the address of the first character, if any. You can't load before you know that what you load is valid. Btw. zero-terminated strings allow you to load unconditionally. Sometimes that's nice.
  - thaumasiotes 4y ago
    OK, but now the difference in how complicated it is to read from the string boils down to this: 1. Read the first chunk of the string length. 2. Is it more than 0? vs 1. Read the first chunk of the string length. 2. Did we get the whole thing? 3. Is the length more than 0? That extra step in the variable-length case means checking whether a bit is set in the value you just read. --- Also, it occurs to me that this whole discussion is talking about how to serialize or deserialize a string, when the original discussion is over how the string should be represented in memory.

thaumasiotes 4y ago

> Flexible width encoding is more complicated compared to simple member access to get at the first character. I don't think this is true either. It's almost true. But what happens if the string length is 0? If you make the assumption that you can access the first character of a zero-length string by just grabbing whatever is in memory after the string header, you're going to make the exact mistake the length field is there to stop you from making, a memory access violation. You have to process the length field in order to do any access at all; many strings don't have a first character. > And how do you handle construction of a string whose size you don't know yet? You might have to move the string away to make space for a bigger string length field. That's true; you'll either need to be willing to store the character data and the length metadata in separate locations, or you'll need to be willing to occasionally move the data around.

jstimpfle 4y ago
Obviously I mean get at the address of the first character, if any. You can't load before you know that what you load is valid. Btw. zero-terminated strings allow you to load unconditionally. Sometimes that's nice.
- thaumasiotes 4y ago
  OK, but now the difference in how complicated it is to read from the string boils down to this: 1. Read the first chunk of the string length. 2. Is it more than 0? vs 1. Read the first chunk of the string length. 2. Did we get the whole thing? 3. Is the length more than 0? That extra step in the variable-length case means checking whether a bit is set in the value you just read. --- Also, it occurs to me that this whole discussion is talking about how to serialize or deserialize a string, when the original discussion is over how the string should be represented in memory.