Is there any way to look something up in a Table using a pre-computed Hash value?
OK, so basically let's say we have a Table and we're either trying to retrieve a value using a specific key, or trying to see if our Table contains a specific key. The normal way I guess would be with a call to hasKey. Now, what if we're - possibly - going to perform the same lookup many times? Wouldn't it be more practical instead of doing Table.hasKey(someKey) and having the hash value of someKey calculated over and over again, to be able to do a lookup by Hash value? (provided I've already calculated it and stored it somewhere) Is it even possible? (I've been looking in the sources and specifically into rawGetImpl() from lib/pure/collections/hashcommon.nim, but still not sure how it would be possible to circumvent this
Re: Force mutable Seq returns
What would you think of using... ?: type SeqRef[T] = ref seq[T] proc newSeq[T](s:seq[T]): SeqRef[T] = new(result) result[] = s Run
Re: Karax Components
Thanks for the sample! Do you use this xName naming convention to make procs look more like types? Makes sense, just clarifying. Also, how would you handle state in your app model?
Re: NaN tagging in Nim?
You could have tables-of-refs-to-objects, e.g. allInts:@seq[int], allFloat:@seq[float], and NaN tag the indices to those lists; it would require one more redirection to actually get the value, but would otherwise work well with any gc. Also, subnormals (neé denormals) are also useful for tagging. And unlike NaNs which could be a result of a computation (e.g. 0.0/0.0) which you must differentiate from your tagged values, if you set the FPU "flush to zero" mode, they will not be generated as a result of a computation; see e.g. [https://stackoverflow.com/questions/54531425/is-it-possible-in-floating-point-to-return-0-0-subtracting-two-different-values/54532647#54532647](https://stackoverflow.com/questions/54531425/is-it-possible-in-floating-point-to-return-0-0-subtracting-two-different-values/54532647#54532647)
Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``
Thank you, Vindaar. That's very helpful!
Re: Karax Components
You can use components with local state, but I haven't experimented with them, I'm more than fine with functions and variables, each in their own file: [https://github.com/kidandcat/nimforum2](https://github.com/kidandcat/nimforum2)
Re: Differences between simple assignment, shallowCopy and deepCopy
deepCopy has value independent of memory management. I don't use it much, if it's not a problem I'd vote for it to remain.
Re: Force mutable Seq returns
Pass the sequence to `shallow()` before processing or create a custom object
type MyShallowSeq[T] {.shallow.} = object
buffer: seq[T]
Run
Your solution will create 2 pointer indirections, it's idiomatic but slower.
Karax Components
I've tried exploring component-based architecture in Karax once: [https://moigagoo.svbtle.com/exploring-karax](https://moigagoo.svbtle.com/exploring-karax) However, I now see there is VCompoment type in Karax and there are examples/tests that demonstrate its usage. Is this the official way to have components in Karax now? Is there any project I could look at built with these components? There's so little information available in Karax repo, the docs don't exist, and there's no sample project. It's a shame, Karax deserves better.
Re: How to avoid recursive module dependency ?
I second dom96, recursive module dependency is a sign of bad code organization. Avoid it.
Re: Web pages with data entry in unicode and unidecode
Looks cool!
Re: Force mutable Seq returns
I was thinking of packaging the seq in a ref object, and then move those ref objects around. but wouldn't that be an overkill?
Re: Force mutable Seq returns
But this makes a copy of the sequence, doesn't it? Is there any way to do the same thing, using the reference? (after all, it's a pointer, if I'm not mistaken... all I want to do is change the value/sequence to which that pointer is pointing)
Force mutable Seq returns
I have a template like this: template ARR(v:Val):seq[Val] = cast[seq[Val]](bitand(v,bitnot(UNMASK))) Run however, I want to be able to change the result like : a = ARR(x) a[0] = Run How can I return a var seq[Val] (or sth like that) ?
Re: Force mutable Seq returns
`var a: seq[Val] a = ARR(x) a[0] = ` Run
Re: How to avoid recursive module dependency ?
Second that, `include` will effectively duplicate your type declarations and will probably cause your code to get ambiguous symbol warnings.
Re: How to avoid recursive module dependency ?
I would strongly recommend avoiding `include` as much as possible, and in particular in this case. What works usually is to create a module for your types, or to think about how you structure your program, usually you will see that you aren't organising your code in the best way.
Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``
Sorry, I didn't see the post before.
You're almost there. There's two small things missing in your code.
1. you should add a newline to the string you write to the input stream. cat
wants that newline
2. instead of closing the input stream, you flush it.
Note however that with cat at least the output stream will never be "done". So
you need some stopping criteria.
import osproc, streams
proc cat(strs: seq[string]): string =
var command = "cat"
var p = startProcess(command, options = {poUsePath})
var inp = inputStream(p)
var outp = outputStream(p)
for str in strs:
# append a new line!
inp.write(str & "\n")
# make sure to flush the stream!
inp.flush()
var line = ""
var happy = 0
while p.running:
if happy == strs.len:
# with `cat` there will always theoretically be data coming from the
stream, so
# we have some artificial stopping criterium (maybe just Ctrl-C)
break
elif outp.readLine(line):
result.add(line & "\n")
inc happy
close(p)
echo cat(@["hello", "world"])
Run
Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``
Still hoping someone can offer some insight on the use of inputStream. Is the documentation simply wrong on this point?
Re: Jester memory usage keep rising using sqlite
In c it depends which allocator you use. Most people don't use the default malloc because it's slow. They have a layer above it which uses it for big chunks while using internal thing for small chunks. For really big chunks Nim will use the standard is malloc and they will free back. This does not happen in web servers.
Re: Jester memory usage keep rising using sqlite
No, the memory will be released to the OS.
Re: Jester memory usage keep rising using sqlite
The GC does release memory under certain [circumstances](https://github.com/nim-lang/Nim/blob/b07694cd90ab7c6eb4660971ddb818b461d4eed8/lib/system/alloc.nim#L861). The code is rather hard to follow though, and I'm not sure _when_ exactly would the GC release memory back to OS. But if you allocate a 2GB string then discard it, the GC will later collect that memory and release it to the OS (this can be forced via a call to `GC_fullCollect`).
Re: Jester memory usage keep rising using sqlite
Is this true with manual memory management as well, or just the built-in memory management and GC? Like, if you were to, say, manually allocate space to load and copy/resize a 20 megapixel photo, will the app continue to occupy 200 MB of RAM even after the memory is released by the app?
Re: Binary resulting much larger with --opt:size?
\--opt:speed implies -O3| ---|--- \--opt:size implies -Os| passing -O4 will impli -O3 It's either -O3 or -Os, you can't have both at the same time hence the conflict. Now it seems like there might still be an issue but without reproducible example it's hard to investigate. You can check with bloaty ([https://github.com/google/bloaty](https://github.com/google/bloaty)) to have an idea if it's just text symbols that are taking space or if it's actual code for example.
Re: Binary resulting much larger with --opt:size?
I don't think they are interfering. The -O4 option is only set for speed and I'm getting the exact same result (900+KB vs 600+KB) even after completely removing it.
Re: NaN tagging in Nim?
Hmm... I see your point. But then how would I be able to store an object's
address? (perhaps, the solution would be to use no GC whatsoever which is
pretty much what I'm doing?)
Btw... here is an experimental implementation of NaN-tagging I've just written
(roughly based on this article:
[https://nikic.github.io/2012/02/02/Pointer-magic-for-efficient-dynamic-value-representations.html)](https://nikic.github.io/2012/02/02/Pointer-magic-for-efficient-dynamic-value-representations.html\)).
I believe it's working though I haven't had time to thoroughly test it.
**Code:**
import bitops
type
ObjType = enum
strObj, arrObj
Obj = ref object
case kind: ObjType:
of strObj: s: string
of arrObj: a: seq[Obj]
Val {.final,union,pure.} = object
asDouble: float64
asBits: int64
const MaxDouble = cast[int64](0xfff8)
const Int32Tag = cast[int64](0xfff9)
const PtrTag= cast[int64](0xfffa)
proc newVal(num:int64): Val {.inline.} =
Val(asBits: bitor(num,Int32Tag))
proc newVal(num: float64): Val {.inline.} =
Val(asDouble:num)
proc newVal(obj: Obj): Val {.inline.} =
Val(asBits: bitor(cast[int64](obj),PtrTag))
proc isDouble(v: Val): bool {.inline.} =
v.asBits < MaxDouble
proc isInt32(v: Val): bool {.inline.} =
bitand(v.asBits,Int32Tag) == Int32Tag
proc isObj(v: Val): bool {.inline.} =
bitand(v.asBits,PtrTag) == PtrTag
proc getDouble(v: Val): float64 {.inline.} =
v.asDouble
proc getInt32(v: Val): int32 {.inline.} =
cast[int32](bitand(v.asBits,bitnot(Int32Tag)))
proc getObj(v: Val): Obj {.inline.} =
result = cast[Obj](bitand(v.asBits,bitNot(PtrTag)))
let a = newVal(32)
echo a.getInt32()
let b = newVal(34.53)
echo b.getDouble()
let c = newVal(Obj(kind:strObj, s:"hello"))
echo c.getObj().s
Run
**Output:**
32
34.53
hello
Run
Re: Binary resulting much larger with --opt:size?
`-O4` will conflict with building for size `-Os`
Re: NaN tagging in Nim?
Don't cast ref objects unless the underlying representation is compatible (seq[byte] and strings). Definitely don't cast ref objects to int. How would the garbage collector collect that?
Re: NaN tagging in Nim?
Do you see anything wrong (particularly memory-safety-wise) with this code? let v = Value(kind: stringValue, s: "hello") let z = cast[int](v) echo repr(cast[Value](z)) echo cast[Value](z).stringify() Run
Re: NaN tagging in Nim?
I've yet to see such code for Nim, but Nim's `cast` is well prepared for it.
Re: Binary resulting much larger with --opt:size?
The only difference is the `-d:mini` flag, you don't use `--opt:size`.
Re: Differences between simple assignment, shallowCopy and deepCopy
In additon to what @mratsim said both `shallowCopy` and `deepCopy` will likely be deprecated. `shallowCopy(x, y)` should have been `x = move(y)` and `deepCopy` should be something like `send` (send data to a different thread).
