type-inference

问题 In programming language what is the difference between Inferred Type and Dynamic typing? I know about Dynamic typing but don't get how dynamic typing is differ from Inferred Type and how? Could someone please provide explanation with some example? 回答1: Inferred type = set ONCE and at compile time. Actually the inferred part is only a time saver in that you don't have to type the Typename IF the compiler can figure it out. Type Inference is often used in conjunction static typing (as is the

问题 Why doesn't defining a variable with auto keyword carry the constexpr 'ness of the expression used to initialize it? As an example, consider the following code: #include <string_view> constexpr std::string_view f() { return "hello"; } static constexpr std::string_view g() { constexpr auto x = f(); // (*) return x.substr(1, 3); } int foo() { return g().length(); } With GCC 10.2 and --std=c++20 -fsanitize=undefined -O3 , this compiles into: foo(): mov eax, 3 ret But if we remove the constexpr

问题 I have a very simple snipper of Spark code which was working on Scala 2.11 and stop compiling after 2.12. import spark.implicits._ val ds = Seq("val").toDF("col1") ds.foreachPartition(part => { part.foreach(println) }) It fails with the error: Error:(22, 12) value foreach is not a member of Object part.foreach(println) The workaround is to help the compiler with such code: import spark.implicits._ val ds = Seq("val").toDF("col1") println(ds.getClass) ds.foreachPartition((part: Iterator[Row])

问题 I have a method that writes one of my classes Foo , which is defined as Thrift, in Parquet form. import Foo import org.apache.spark.rdd.RDD import org.apache.thrift.TBase import org.apache.hadoop.mapreduce.Job import org.apache.parquet.hadoop.ParquetOutputFormat import org.apache.parquet.hadoop.thrift.ParquetThriftOutputFormat def writeThriftParquet(rdd: RDD[Foo], outputPath: String): Unit = { val job = Job.getInstance() ParquetThriftOutputFormat.setThriftClass(job, classOf[Foo])

问题 How to safely type curried functions in typescript? With particular regard to the following example interface Prop { <T, K extends keyof T>(name: K, object: T): T[K]; <K>(name: K): <T>(object: T) => /* ?? */; } const prop: Prop = (key, object) => object[key]; const valid1 = prop('foo', { foo: 'hello' }); // string const valid = prop('foo')({ foo: 'hello' }); // string // `never`, since `baz` does not exist in { foo: string } const invalid = prop('baz')({ foo: 'hello' }); // never 回答1:

问题 How to safely type curried functions in typescript? With particular regard to the following example interface Prop { <T, K extends keyof T>(name: K, object: T): T[K]; <K>(name: K): <T>(object: T) => /* ?? */; } const prop: Prop = (key, object) => object[key]; const valid1 = prop('foo', { foo: 'hello' }); // string const valid = prop('foo')({ foo: 'hello' }); // string // `never`, since `baz` does not exist in { foo: string } const invalid = prop('baz')({ foo: 'hello' }); // never 回答1:

问题 How to safely type curried functions in typescript? With particular regard to the following example interface Prop { <T, K extends keyof T>(name: K, object: T): T[K]; <K>(name: K): <T>(object: T) => /* ?? */; } const prop: Prop = (key, object) => object[key]; const valid1 = prop('foo', { foo: 'hello' }); // string const valid = prop('foo')({ foo: 'hello' }); // string // `never`, since `baz` does not exist in { foo: string } const invalid = prop('baz')({ foo: 'hello' }); // never 回答1:

问题 How to safely type curried functions in typescript? With particular regard to the following example interface Prop { <T, K extends keyof T>(name: K, object: T): T[K]; <K>(name: K): <T>(object: T) => /* ?? */; } const prop: Prop = (key, object) => object[key]; const valid1 = prop('foo', { foo: 'hello' }); // string const valid = prop('foo')({ foo: 'hello' }); // string // `never`, since `baz` does not exist in { foo: string } const invalid = prop('baz')({ foo: 'hello' }); // never 回答1:

问题 I have the following simple code piece: List<XXXXBean> queryPeriodData() { if (CollectionUtils.isEmpty(res)) { return Collections.emptyList(); } return res; } It works. but if I change to this, there is a compile error... return CollectionUtils.isEmpty(res) ? Collections.emptyList() : res; error message is "Type mismatch: cannot convert from List< capture#1-of ? extends Object> to List< XXXXBean>" I don't know the difference between the two way. 回答1: try Collections.<XXXXBean>emptyList() in

问题 This question already has answers here : Partial generic type inference possible in C#? (5 answers) Closed 2 years ago . I have the following method public bool HasTypeAttribute<TAttribute, TType>(TType obj) { return typeof(TType).GetCustomAttribute<TAttribute>() != null; } and I want to be able to use it like this: MyClass instance = new MyClass(); TypeHelper.HasTypeAttribute<SerializableAttribute>(instance); but I can't get it working because of the incorrect number of type parameters so