type-promotion

问题 I'm trying to understand the implicit conversion rules in C++ and I understood that when there are one operation between two primary types the "lower type" is promoted to the "higher type", so let say for: int a = 5; float b = 0.5; std::cout << a + b << "\n"; should print 5.5 because 'a' gets promoted to float type. I also understood that unsigned types are "higher types" than the signed counter parts so: int c = 5; unsigned int d = 10; std::cout << c - d << "\n"; prints 4294967291 because 'c

问题 I'm trying to understand the implicit conversion rules in C++ and I understood that when there are one operation between two primary types the "lower type" is promoted to the "higher type", so let say for: int a = 5; float b = 0.5; std::cout << a + b << "\n"; should print 5.5 because 'a' gets promoted to float type. I also understood that unsigned types are "higher types" than the signed counter parts so: int c = 5; unsigned int d = 10; std::cout << c - d << "\n"; prints 4294967291 because 'c

问题 I'm upgrading a personal package that is based on the Flutter framework. I noticed here in the Flutter Text widget source code that there is a null check: if (textSpan != null) { properties.add(textSpan!.toDiagnosticsNode(name: 'textSpan', style: DiagnosticsTreeStyle.transition)); } However, textSpan! is still using the ! operator. Shouldn't textSpan be promoted to a non-nullable type without having to use the ! operator? However, trying to remove the operator gives the following error: An

问题 I'm upgrading a personal package that is based on the Flutter framework. I noticed here in the Flutter Text widget source code that there is a null check: if (textSpan != null) { properties.add(textSpan!.toDiagnosticsNode(name: 'textSpan', style: DiagnosticsTreeStyle.transition)); } However, textSpan! is still using the ! operator. Shouldn't textSpan be promoted to a non-nullable type without having to use the ! operator? However, trying to remove the operator gives the following error: An

问题 There is a great paper on C++ for scientific computing where the author (T. Veldhuizen) suggests a traits-based approach to address type promotion. I have used such approach, and found it effective: #include<iostream> #include<complex> #include<typeinfo> template<typename T1, typename T2> struct promote_trait{}; #define DECLARE_PROMOTION(A, B, C) template<> struct promote_trait<A, B> { using T_promote = C;}; DECLARE_PROMOTION(int, char, int); DECLARE_PROMOTION(int, float, float); DECLARE

问题 I know in C and Java, float's underlying representation is IEEE754-32, double is IEEE754-64. In expressions, float will be auto-promoted to double . So how? Take 3.7f for example. Is the process like this? 3.7f will be represented in memory using IEEE754. It fits in 4 bytes. During calculation, it may be loaded into a 64-bit register (or whatever 64-bit place), turning the 3.7f into IEEE754-64 represent. 回答1: It is very implementation-dependent. For one example, on x86 platform the set of FPU

问题 I've into curious question (asking it myself while reading a crude piece of code). Let's look at expression: double a = c*d*e*2/3*f; where c, d, e, f are initialized variables of type double . Does standard guarantee that it would be treated as c*d*e*2 (double result) then divided by 3 and multiplied by f (or some similar behavior). Obviously, 2/3 being calculated to 0 is undesirable. Which paragraph of standard defines that? 回答1: Based on the standard [intro.abstract] - Note 7 (non-normative

问题 I'm looking for an explanation of the following, If I run something like this I get an unknown type, SELECT pg_typeof(a) FROM ( SELECT null ) AS t(a); pg_typeof ----------- unknown (1 row) However, with more complexity it becomes text magically, SELECT pg_typeof(a) FROM ( SELECT null UNION SELECT null ) AS t(a); pg_typeof ----------- text (1 row) Explicit casting doesn't change that, this also returns text , SELECT pg_typeof(a) FROM ( SELECT null::unknown UNION SELECT null::unknown ) AS t(a);

问题 Consider following program: #include <stdio.h> int main() { short a=9; //printf("%hi\n",a); printf("%d",a); // LINE 6 } According to this the format specifier for short type (signed) is %hi Is the short type variable always gets promoted automatically to int before performing any operation on it? Is it undefined behavior , If I use %d format specifier to print the value of variable in this program? I compiled it using gcc -Wall -Wextra -WFormat options but still compiler isn't showing any

问题 I recently discovered the Data.Promotion half of singletons. It has loads of type families which allow essentially arbitrary computation at the type level. I have a couple of questions about usage: What is the difference between ($), (%$), ($$), and are they related to :++$ , :.$ , etc? Are these actually infix operators? I was under the impression all infix type constructors had to begin with a : . I'm trying to map a constructor over a list: {-# LANGUAGE DataKinds, TypeOperators, PolyKinds