https://github.com/antirez/sds
The trick is the size is hidden before the adress of the buffer.("Learn this one simple trick that will change your life for ever").
From the Readme:
```
Advantage #1: you can pass SDS strings to functions designed for C functions without accessing a struct member or calling a function
Advantage #2: accessing individual chars is straightforward.
Advantage #3: single allocation has better cache locality. Usually when you access a string created by a string library using a structure, you have two different allocations for the structure representing the string, and the actual buffer holding the string. Over the time the buffer is reallocated, and it is likely that it ends in a totally different part of memory compared to the structure itself. Since modern programs performances are often dominated by cache misses, SDS may perform better in many workloads.
```