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How to not rewrite it in Rust

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Re: How to not rewrite it in Rust

#21

Post by infogulch »

readams wrote: post #16
beefhash wrote: post #9

Earlier quoted context omitted.

The tree only contains configure.in, not the generated configure output, and Makefile.am, not the generated Makefile.in. You do need the entire autotools suite installed for it to build. Why they published it like this is beyond me, however. The whole point of autotools is not making your users install them (unlike CMake and virtually every other build system for C there is).

That's not true. If you build from a dist tarball, you do not need auto tools installed. You usually do if you build from a git repo, however.

How/why is a dist tarball not exactly the same as a zipped up git tree?

Re: How to not rewrite it in Rust

#22

Post by zeroxfe »

mmaurizi wrote: post #19
fmakunbound wrote: post #12

> Rust gives you the power to do things which would be unheard of (or just plain dangerous) in other languages What are examples of the unheard of things?

Passing around pointers to objects on the stack. In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all. In rust, the compiler will statically determine if a pointer to an object on the stack could escape the function, and if so will fail to compile.

> In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all.

Just a nitpick, this is only true for non-garbage-collected (or refcounted) languages. :-)

Re: How to not rewrite it in Rust

#24

Post by aisengard »

StreamBright wrote: post #20
steveklabnik wrote: post #8

Earlier quoted context omitted.

All of Rust's complexity for strings comes out of complexity due to UTF-8. Well, a tiny bit comes from the fact that Rust has pointers too, but most of it is UTF-8. Did you happen to read the book? We cover strings early because this is a common pain point. Also, if you have something more detailed than "get strings out of libraries", I can give better advice. It's tough to tell what the actual issue is.

Like this: use sha2::{Sha256, Digest}; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result(); ?? } How do I get a string with the hash value? Which chapter of which book should I read?

The hash value is a bunch of bytes. A "string" would need to be some encoded version of those bytes, commonly hexadecimal representation.

Re: How to not rewrite it in Rust

#25

Post by chousuke »

StreamBright wrote: post #20
steveklabnik wrote: post #8

Earlier quoted context omitted.

All of Rust's complexity for strings comes out of complexity due to UTF-8. Well, a tiny bit comes from the fact that Rust has pointers too, but most of it is UTF-8. Did you happen to read the book? We cover strings early because this is a common pain point. Also, if you have something more detailed than "get strings out of libraries", I can give better advice. It's tough to tell what the actual issue is.

Like this: use sha2::{Sha256, Digest}; fn main() { let mut hasher = Sha256::new(); hasher.input(b"hello world"); let result = hasher.result(); ?? } How do I get a string with the hash value? Which chapter of which book should I read?

I think you can use format!() to format the byte array as a hex string.

The result of a hash is never a string, so it makes sense that you'd need another step to print it as one.

Re: How to not rewrite it in Rust

#26

Post by lmkg »

zeroxfe wrote: post #22
mmaurizi wrote: post #19

Earlier quoted context omitted.

Passing around pointers to objects on the stack. In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all. In rust, the compiler will statically determine if a pointer to an object on the stack could escape the function, and if so will fail to compile.

> In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all. Just a nitpick, this is only true for non-garbage-collected (or refcounted) languages. :-)

Well, if you're gonna nitpick...

A garbage-collected language wouldn't let you allocate such items on the stack in the first place.

GC languages tend not to let you choose where to allocate in the first place, and have obligatory heap semantics for reference types. Some compilers (including Go and Java, to my knowledge) will attempt to optimize the implementation to stack allocation when possible using escape analysis, but this is less precise, and more opaque, then Rust's allocation. And you won't get feedback if it stops working.

So, by GP's comment of "unheard of (or just plain dangerous)", the "unheard-of" applies to GC languages and "plain dangerous" would apply non-GC languages.

Re: How to not rewrite it in Rust

#27

Post by baq »

StreamBright wrote: post #6

I still have issues with Rust string handling. Half of the time I have no idea how to get strings out of libraries. I don't understand the intentions of the language creators at all. Does anybody have a great intro to Rust for software engineers who come from Python or something similar where high level types are the norm?

It’s like that because strings are very difficult to get 100% right even in gced languages (Python 2 says hello) and when you take into account ownership and different standards used even in the same OS it all becomes a nightmare. You have to know when you want a reference or an owned object, when you want mutable vs immutable and when you want portable vs OS specific, and god forbid you put a path in a string. This is why rust has multiple string type families, all of which (well, most) Python very conveniently hides, for good reasons.

Re: How to not rewrite it in Rust

#28

Post by fluffything »

zeroxfe wrote: post #22
mmaurizi wrote: post #19

Earlier quoted context omitted.

Passing around pointers to objects on the stack. In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all. In rust, the compiler will statically determine if a pointer to an object on the stack could escape the function, and if so will fail to compile.

> In another language you'd risk having a pointer to invalid memory when the function returns if the pointer escapes the function, and so it is advised to use pointers to objects on the stack sparingly if at all. Just a nitpick, this is only true for non-garbage-collected (or refcounted) languages. :-)

Which garbage-collected languages put automatic variables in an actual stack that gets bumped on function calls even when you pass pointers to the automatic variables ?

Re: How to not rewrite it in Rust

#29

Post by lmkg »

steveklabnik wrote: post #15
cannam wrote: post #13

Earlier quoted context omitted.

Surely "How Not To..." is typically used when you're talking of a bad way to do something, or a way to fail - so this sounds like it's describing a bad way to rewrite something in Rust, which is not the case. It also isn't the wording used in the original article title.

> so this sounds like it's describing a bad way to rewrite something in Rust, which is not the case. I think this kind of title is trying to do exactly that, or at least, that's how I took it. > It also isn't the wording used in the original article title. This is a good reason to switch it, for sure. I didn't realize this, if you had led with that, I wouldn't have said anything :)

> I think this kind of title is trying to do exactly that, or at least, that's how I took it

I took the exact opposite: This article is describing an alternative to RiiR, so that RiiR is avoided when not needed.

Re: How to not rewrite it in Rust

#30

Post by fjp »

steveklabnik wrote: post #8
StreamBright wrote: post #6

I still have issues with Rust string handling. Half of the time I have no idea how to get strings out of libraries. I don't understand the intentions of the language creators at all. Does anybody have a great intro to Rust for software engineers who come from Python or something similar where high level types are the norm?

All of Rust's complexity for strings comes out of complexity due to UTF-8. Well, a tiny bit comes from the fact that Rust has pointers too, but most of it is UTF-8. Did you happen to read the book? We cover strings early because this is a common pain point. Also, if you have something more detailed than "get strings out of libraries", I can give better advice. It's tough to tell what the actual issue is.

Which book? I'm just starting the O'Reilly book, coming from Python
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