book | The Rust Programming Language | Learning library
kandi X-RAY | book Summary
kandi X-RAY | book Summary
The Rust Programming Language
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of book
book Key Features
book Examples and Code Snippets
const isEmpty = val => val == null || !(Object.keys(val) || val).length;
isEmpty([]); // true
isEmpty({}); // true
isEmpty(''); // true
isEmpty([1, 2]); // false
isEmpty({ a: 1, b: 2 }); // false
isEmpty('text'); // false
isEmpty(123); // true -
const geometricProgression = (end, start = 1, step = 2) =>
Array.from({
length: Math.floor(Math.log(end / start) / Math.log(step)) + 1,
}).map((_, i) => start * step ** i);
geometricProgression(256); // [1, 2, 4, 8, 16, 32, 64, 128, 2
const includesAny = (arr, values) => values.some(v => arr.includes(v));
includesAny([1, 2, 3, 4], [2, 9]); // true
includesAny([1, 2, 3, 4], [8, 9]); // false
public void update(Book book) throws BookNotFoundException, VersionMismatchException {
if (!collection.containsKey(book.getId())) {
throw new BookNotFoundException("Not found book with id: " + book.getId());
}
var latestBook = coll
public void bookRoom(int roomNumber) throws Exception {
var room = hotelDao.getById(roomNumber);
if (room.isEmpty()) {
throw new Exception("Room number: " + roomNumber + " does not exist");
} else {
if (room.get().isBooked()
@Override
public Book getBook(String title) {
Book bookDTo;
try (var session = sessionFactory.openSession()) {
var sqlQuery = session.createSQLQuery("SELECT b.title as \"title\","
+ " b.price as \"price\"" + " FROM Book b wh
Community Discussions
Trending Discussions on book
QUESTION
I am trying to use a custom allocator, using the allocator API in Rust.
It seems Rust considers Vec
and Vec
as two distinct types.
ANSWER
Answered 2022-Mar-28 at 09:53Update:
Since GitHub pull request #93755 has been merged, comparison between Vec
s with different allocators is now possible.
Original answer:
Vec
uses the std::alloc::Global
allocator by default, so Vec
is in fact Vec
. Since Vec
and Vec
are indeed distinct types, they cannot directly be compared because the PartialEq
implementation is not generic for the allocator type. As @PitaJ commented, you can compare the slices instead using assert_eq!(&a[..], &b[..])
(which is also what the author of the allocator API recommends).
QUESTION
Is there a way to obtain the greatest value representable by the floating-point type float
which is smaller than 1
.
ANSWER
Answered 2022-Mar-08 at 23:51You can use the std::nextafter
function, which, despite its name, can retrieve the next representable value that is arithmetically before a given starting point, by using an appropriate to
argument. (Often -Infinity
, 0
, or +Infinity
).
This works portably by definition of nextafter
, regardless of what floating-point format your C++ implementation uses. (Binary vs. decimal, or width of mantissa aka significand, or anything else.)
Example: Retrieving the closest value less than 1 for the double
type (on Windows, using the clang-cl compiler in Visual Studio 2019), the answer is different from the result of the 1 - ε
calculation (which as discussed in comments, is incorrect for IEEE754 numbers; below any power of 2, representable numbers are twice as close together as above it):
QUESTION
Room database is not working in mac book pro m1 i have already added id 'kotlin-kapt'
screen shoot of android studio console log
...
- What went wrong: Execution failed for task ':app:kaptDebugKotlin'.
A failure occurred while executing org.jetbrains.kotlin.gradle.internal.KaptWithoutKotlincTask$KaptExecutionWorkAction java.lang.reflect.InvocationTargetException (no error message)
Caused by: java.lang.reflect.InvocationTargetException at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at org.jetbrains.kotlin.kapt3.base.AnnotationProcessingKt.doAnnotationProcessing(annotationProcessing.kt:90) at org.jetbrains.kotlin.kapt3.base.AnnotationProcessingKt.doAnnotationProcessing$default(annotationProcessing.kt:31) at org.jetbrains.kotlin.kapt3.base.Kapt.kapt(Kapt.kt:45) ... 31 more
Caused by: java.lang.Exception: No native library is found for os.name=Mac and os.arch=aarch64. path=/org/sqlite/native/Mac/aarch64 at org.sqlite.SQLiteJDBCLoader.loadSQLiteNativeLibrary(SQLiteJDBCLoader.java:333) at org.sqlite.SQLiteJDBCLoader.initialize(SQLiteJDBCLoader.java:64) at androidx.room.verifier.DatabaseVerifier.(DatabaseVerifier.kt:71) ... 50 more
ANSWER
Answered 2021-Nov-28 at 16:03Simply use Room 2.4.0-alpha03
QUESTION
I am reading this book by Fedor Pikus and he has some very very interesting examples which for me were a surprise.
Particularly this benchmark caught me, where the only difference is that in one of them we use || in if and in another we use |.
ANSWER
Answered 2022-Feb-08 at 19:57Code readability, short-circuiting and it is not guaranteed that Ord will always outperform a ||
operand.
Computer systems are more complicated than expected, even though they are man-made.
There was a case where a for loop with a much more complicated condition ran faster on an IBM. The CPU didn't cool and thus instructions were executed faster, that was a possible reason. What I am trying to say, focus on other areas to improve code than fighting small-cases which will differ depending on the CPU and the boolean evaluation (compiler optimizations).
QUESTION
Whenever I am trying to run the docker images, it is exiting in immediately.
...ANSWER
Answered 2021-Aug-22 at 15:41Since you're already using Docker
, I'd suggest using a multi-stage build. Using a standard docker image like golang
one can build an executable asset which is guaranteed to work with other docker linux images:
QUESTION
There are so many ways to define colour scales within ggplot2
. After just loading ggplot2
I count 22
functions beginging with scale_color_*
(or scale_colour_*
) and same number beginging with scale_fill_*
. Is it possible to briefly name the purpose of the functions below? Particularly I struggle with the differences of some of the functions and when to use them.
- scale_*_binned()
- scale_*_brewer()
- scale_*_continuous()
- scale_*_date()
- scale_*_datetime()
- scale_*_discrete()
- scale_*_distiller()
- scale_*_fermenter()
- scale_*_gradient()
- scale_*_gradient2()
- scale_*_gradientn()
- scale_*_grey()
- scale_*_hue()
- scale_*_identity()
- scale_*_manual()
- scale_*_ordinal()
- scale_*_steps()
- scale_*_steps2()
- scale_*_stepsn()
- scale_*_viridis_b()
- scale_*_viridis_c()
- scale_*_viridis_d()
What I tried
I've tried to make some research on the web but the more I read the more I get onfused. To drop some random example: "The default scale for continuous fill scales is scale_fill_continuous()
which in turn defaults to scale_fill_gradient()
". I do not get what the difference of both functions is. Again, this is just an example. Same is true for scale_color_binned()
and scale_color_discrete()
where I can not name the difference. And in case of scale_color_date()
and scale_color_datetime()
the destription says "scale_*_gradient
creates a two colour gradient (low-high), scale_*_gradient2
creates a diverging colour gradient (low-mid-high), scale_*_gradientn
creates a n-colour gradient." which is nice to know but how is this related to scale_color_date()
and scale_color_datetime()
? Looking for those functions on the web does not give me very informative sources either. Reading on this topic gets also chaotic because there are tons of color palettes in different packages which are sequential/ diverging/ qualitative plus one can set same color in different ways, i.e. by color name, rgb, number, hex code or palette name. In part this is not directly related to the question about the 2*22
functions but in some cases it is because providing a "wrong" palette results in an error (e.g. the error"Continuous value supplied to discrete scale
).
Why I ask this
I need to do many plots for my work and I am supposed to provide some function that returns all kind of plots. The plots are supposed to have similiar layout so that they fit well together. One aspect I need to consider here is that the colour scales of the plots go well together. See here for example, where so many different kind of plots have same colour scale. I was hoping I could use some general function which provides a colour palette to any data, regardless of whether the data is continuous or categorical, whether it is a fill or col easthetic. But since this is not how colour scales are defined in ggplot2
I need to understand what all those functions are good for.
ANSWER
Answered 2022-Feb-01 at 18:14This is a good question... and I would have hoped there would be a practical guide somewhere. One could question if SO would be a good place to ask this question, but regardless, here's my attempt to summarize the various scale_color_*()
and scale_fill_*()
functions built into ggplot2
. Here, we'll describe the range of functions using scale_color_*()
; however, the same general rules will apply for scale_fill_*()
functions.
There are 22 functions in all, but happily we can group them intelligently based on practical usage scenarios. There are three key criteria that can be used to define practically how to use each of the scale_color_*()
functions:
Nature of the mapping data. Is the data mapped to the color aesthetic discrete or continuous? CONTINUOUS data is something that can be explained via real numbers: time, temperature, lengths - these are all continuous because even if your observations are
1
and2
, there can exist something that would have a theoretical value of1.5
. DISCRETE data is just the opposite: you cannot express this data via real numbers. Take, for example, if your observations were:"Model A"
and"Model B"
. There is no obvious way to express something in-between those two. As such, you can only represent these as single colors or numbers.The Colorspace. The color palette used to draw onto the plot. By default,
ggplot2
uses (I believe) a color palette based on evenly-spaced hue values. There are other functions built into the library that use either Brewer palettes or Viridis colorspaces.The level of Specification. Generally, once you have defined if the scale function is continuous and in what colorspace, you have variation on the level of control or specification the user will need or can specify. A good example of this is the functions:
*_continuous()
,*_gradient()
,*_gradient2()
, and*_gradientn()
.
We can start off with continuous scales. These functions are all used when applied to observations that are continuous variables (see above). The functions here can further be defined if they are either binned or not binned. "Binning" is just a way of grouping ranges of a continuous variable to all be assigned to a particular color. You'll notice the effect of "binning" is to change the legend keys from a "colorbar" to a "steps" legend.
The continuous example (colorbar legend):
QUESTION
I'm reading "Computer Systems: A Programmer's Perspective, 3/E" (CS:APP3e) and the following code is an example from the book:
...ANSWER
Answered 2022-Feb-03 at 04:10(This answer is a summary of comments posted above by Antti Haapala, klutt and Peter Cordes.)
GCC allocates more space than "necessary" in order to ensure that the stack is properly aligned for the call to proc
: the stack pointer must be adjusted by a multiple of 16, plus 8 (i.e. by an odd multiple of 8). Why does the x86-64 / AMD64 System V ABI mandate a 16 byte stack alignment?
What's strange is that the code in the book doesn't do that; the code as shown would violate the ABI and, if proc
actually relies on proper stack alignment (e.g. using aligned SSE2 instructions), it may crash.
So it appears that either the code in the book was incorrectly copied from compiler output, or else the authors of the book are using some unusual compiler flags which alter the ABI.
Modern GCC 11.2 emits nearly identical asm (Godbolt) using -Og -mpreferred-stack-boundary=3 -maccumulate-outgoing-args
, the former of which changes the ABI to maintain only 2^3 byte stack alignment, down from the default 2^4. (Code compiled this way can't safely call anything compiled normally, even standard library functions.) -maccumulate-outgoing-args
used to be the default in older GCC, but modern CPUs have a "stack engine" that makes push/pop single-uop so that option isn't the default anymore; push for stack args saves a bit of code size.
One difference from the book's asm is a movl $0, %eax
before the call, because there's no prototype so the caller has to assume it might be variadic and pass AL = the number of FP args in XMM registers. (A prototype that matches the args passed would prevent that.) The other instructions are all the same, and in the same order as whatever older GCC version the book used, except for choice of registers after call proc
returns: it ends up using movslq %edx, %rdx
instead of cltq
(sign-extend with RAX).
CS:APP 3e global edition is notorious for errors in practice problems introduced by the publisher (not the authors), but apparently this code is present in the North American edition, too. So this may be the author's mistake / choice to use actual compiler output with weird options. Unlike some of the bad global edition practice problems, this code could have come unmodified from some GCC version, but only with non-standard options.
Related: Why does GCC allocate more space than necessary on the stack, beyond what's needed for alignment? - GCC has a missed-optimization bug where it sometimes reserves an additional 16 bytes that it truly didn't need to. That's not what's happening here, though.
QUESTION
Here is a basic Spinlock implemented with std::atomic_flag
.
The author of the book claims that second while in the lock()
boosts performance.
ANSWER
Answered 2022-Jan-28 at 05:13Reading a memory address does not clear the cache line.
Writing does.
So in a modern computer, there is RAM, and there are multiple layers of cache "around" the CPU (they are called L1, L2 and L3 cache, but the important part is that they are layers, and the CPU is at the middle). In a multi-core system, often the outer layers are shared; the innermost layer is usually not, and is specific to a given CPU.
Clearing the cache line means informing every other cache holding this memory "the data you own may be stale, throw it out".
Test and set writes true and atomically returns the old value. It clears the cache line, because it writes.
Test does not write. If you have another thread unsynchronized with this one, it reading the cache of this memory doesn't have to be poked.
The outer loop writes true, and exits if it replaced false. The inner loop waits until there is a false visible, then falls to outer loop. The inner loop need not clear every other cpu's cache status of the value of the atomic flag, but the outer has to (as it could change the false to true). As spinning could go on for a while, avoiding continuous cache clearing seems like a good idea.
QUESTION
I am trying to understand overloading resolution in C++ through the books listed here. One such example that i wrote to clear my concepts whose output i am unable to understand is given below.
...ANSWER
Answered 2022-Jan-25 at 17:19Essentially, skipping over some stuff not relevant in this case, overload resolution is done to choose the user-defined conversion function to initialize the variable and (because there are no other differences between the conversion operators) the best viable one is chosen based on the rank of the standard conversion sequence required to convert the return value of to the variable's type.
The conversion int -> double
is a floating-integral conversion, which has rank conversion.
The conversion float -> double
is a floating-point promotion, which has rank promotion.
The rank promotion is better than the rank conversion, and so overload resolution will choose operator float
as the best viable overload.
The conversion int -> long double
is also a floating-integral conversion.
The conversion float -> long double
is not a floating-point promotion (which only applies for conversion float -> double
). It is instead a floating-point conversion which has rank conversion.
Both sequences now have the same standard conversion sequence rank and also none of the tie-breakers (which I won't go through) applies, so overload resolution is ambigious.
The conversion int -> bool
is a boolean conversion which has rank conversion.
The conversion float -> bool
is also a boolean conversion.
Therefore the same situation as above arises.
See https://en.cppreference.com/w/cpp/language/overload_resolution#Ranking_of_implicit_conversion_sequences and https://en.cppreference.com/w/cpp/language/implicit_conversion for a full list of the conversion categories and ranks.
Although it might seem that a conversion between floating-point types should be considered "better" than a conversion from integral to floating-point type, this is generally not the case.
QUESTION
I came across this term when exploring Rust.
I saw different kinds of explanations regarding this and still don't quite get the ideas.
In The Embedded Rust Book, it said
Type states are also an excellent example of Zero Cost Abstractions
- the ability to move certain behaviors to compile time execution or analysis.
These type states contain no actual data, and are instead used as markers.
Since they contain no data, they have no actual representation in memory at runtime:
Does it mean the runtime is faster because there is no memory in runtime?
Appreciate it if anyone can explain it in an easy to understand way.
...ANSWER
Answered 2021-Sep-14 at 13:11Zero Cost Abstractions means adding higher-level programming concepts, like generics, collections and so on do not come with a run-time cost, only compiler time cost (the code will be slower to compile). Any operation on zero-cost abstractions is as fast as you would write out matching functionality by hand using lower-level programming concepts (for loops, counters, ifs and so on).
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Vulnerabilities
No vulnerabilities reported
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