Strings and the CLR – A Special Relationship

Post by matthewwarren » Wed, Jun 01, 2016, 8:52 AM UTC

MarkSweep wrote: post #4

ygra wrote: post #2

Another point for this, besides optimization, is easier interop with existing technologies. The memory layout is identical to Windows' BSTR, as far as I know, and also includes a terminating U+0000. All of that makes it possible to marshal a CLR string as is in many circumstances without the need to copy or convert the characters around.

There is an amusing comment in the CLR about it's support for odd length BSTRs[0]. There can be an extra wchar after the null terminator to store the extra byte. It looks like if you use the automatic BSTR marshaler it creates a copy[1], though the CLR is so big it's hard for me to say that with confidence. Taking the address of a string with the fixed statement in C# of course won't allocate and that pointer can be…

Post by matthewwarren » Wed, Jun 01, 2016, 11:07 AM UTC

jsingleton wrote: post #12

Nice post. There are many things that aren't possible in C# but can be expressed in pure IL. Sigil [0] is an IL generator used in the high-performance JSON serializer Jil [1], which takes advantage of this. https://github.com/kevin-montrose/Sigil https://github.com/kevin-montrose/Jil

Post by pjmlp » Wed, Jun 01, 2016, 11:11 AM UTC

matthewwarren wrote: post #13

jsingleton wrote: post #12

Nice post. There are many things that aren't possible in C# but can be expressed in pure IL. Sigil [0] is an IL generator used in the high-performance JSON serializer Jil [1], which takes advantage of this. https://github.com/kevin-montrose/Sigil https://github.com/kevin-montrose/Jil

I've seen Jil/Sigil before, but not thought about it in this way. Are you saying that you could exactly replicate a C# System.String using IL, or am I mis-understanding?

Post by masklinn » Wed, Jun 01, 2016, 11:34 AM UTC

Someone wrote: post #6

So, are there high-level languages that make it easy to write classes that include length-varies-by-instance member(s) in their memory layout? That could be a huge efficiency gain because of cache misses.

Post by matthewwarren » Wed, Jun 01, 2016, 11:45 AM UTC

zamalek wrote: post #18

matthewwarren wrote: post #13

Earlier quoted context omitted.

I've seen Jil/Sigil before, but not thought about it in this way. Are you saying that you could exactly replicate a C# System.String using IL, or am I mis-understanding?

I'm not sure if you could replicate System.String, because the oddity is happening at the metadata level - apart from special cases like String, .Net types must be compile-time constant length (if I remember correctly). However, at the instruction level you can do some pretty awesome stuff. This slice[1] library is able to verifiably and safely grab a slice of data out of any arbitrary structure by using a MSIL featu…