Scala

Scala (/ˈskɑːlɑː/ skah-lah) is a general purpose programming language. Scala has full support for functional programming and a very strong static type system. Designed to be concise, many of Scala’s design decisions were inspired by criticism of the shortcomings of Java.
Scala source code is intended to be compiled to Java bytecode, so that the resulting executable code runs on a Java virtual machine. Java libraries may be used directly in Scala code and vice versa (language interoperability). Like Java, Scala is object-oriented, and uses a curly-brace syntax reminiscent of the C programming language. Unlike Java, Scala has many features of functional programming languages like Scheme, Standard ML and Haskell, including currying, type inference, immutability, lazy evaluation, and pattern matching. It also has an advanced type system supporting algebraic data types, covariance and contravariance, higher-order types (but not higher-rank types), and anonymous types. Other features of Scala not present in Java include operator overloading, optional parameters, named parameters, raw strings, and no checked exceptions.
The name Scala is a portmanteau of “scalable” and “language”, signifying that it is designed to grow with the demands of its users.

inliner warnings with Map literal and -optimize

scala在编译&优化的时候,有时候会返回个inline warning.但是,实际上我们写代码已经不能再优化了. 比如如下这个例子:

yu:~ yu$ scala -version
Scala code runner version 2.11.7 -- Copyright 2002-2013, LAMP/EPFL
yu:~ yu$ scala -optimize -Yinline-warnings
Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_05).
Type in expressions to have them evaluated.
Type :help for more information.

scala> object O { Map(
     |   "a" -> 0, "b" -> 1, "c" -> 2, "d" -> 3, "e" -> 4,
     |   "a" -> 0, "b" -> 1, "c" -> 2, "d" -> 3, "e" -> 4,
     |   "a" -> 0, "b" -> 1, "c" -> 2, "d" -> 3, "e" -> 4,
     |   "f" -> 5, "g" -> 6, "h" -> 7, "i" -> 8) }
warning: At the end of the day, could not inline @inline-marked method ->$extension
warning: At the end of the day, could not inline @inline-marked method ->$extension
warning: At the end of the day, could not inline @inline-marked method ->$extension
warning: At the end of the day, could not inline @inline-marked method ->$extension
defined object O

我们可以看到有个issue ,讲的就是这件事.它是12年底建立的,但一直没啥好的回答...可怜我为了关掉这个warning连带好几个其它warning都不能用了.

不过,今年五月终于有结果了.

(more…)

By Yu, ago

a workaround of false negative in missing interpolator warning

一般情况下,我们会倾向于打开各种warning,以便规范我们的代码.不过,scala有时候有些warning也是蛮扯的.比如这么一段

$ scala -Xlint:missing-interpolator
Welcome to Scala version 2.11.7 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_05).
Type in expressions to have them evaluated.
Type :help for more information.

scala> val key="value"; println("$key")
<console>:12: warning: possible missing interpolator: detected interpolated identifier `$key`
        println("$key")
                ^
$key
key: String = value

(more…)

By Yu, ago

scala 读写文件

scala 一般用于网络上消息的处理,比如读写 mongodb, 处理 http request. 但偶尔写个 script, 还是要读写个文件的.

scala 包装了一个 Source 类,可以读取各种来源的数据, url, file 都可以. 但似乎并没有对写数据做什么处理.

(more…)

By Yu, ago