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Functions and Methods ---- {{#x|Functions}} and {{#x|Methods}} 函数和方法 ☺{{#author|agentzh (章亦春)}}☺ {{#date|2006.10}} ---- {{#tag|☆}} {{#ci|Consistent}} interface, {{#ci|Simple}} interface, {{#ci|rich}} interface 一致的接口，简单的接口，丰富的接口 ---- C# seems to have {{#ci|hundreds}} of {{#ci|different}} collection classes, used {{#x|inconsistently}} in the .NET libraries. -- Ned Batchelder C# 似乎拥有成百上千个不同的集合类，它 们在 .NET 类库中的使用是如此的不一致。 ---- {{#x|Perl 6}}'s {{#ci|array}} ➥ {{#ci|Simple}} interface with {{#ci|rich}} functionalities Perl 6 数组：简单的接口，丰富的功能。 ---- {{#cm|# use it as an ordinary array:}} {{#v|@item}} = {{#x|'dog'}}, {{#x|'cat'}}, {{#x|'mouse'}}, {{#x|'tiger'}}; {{#v|@item}}[0].say; {{#cm|# prints 'dog'}} say ~{{#v|@item}}[1..-1]; {{#cm|# prints 'cat mouse tiger'}} {{#v|@item}}[2] = {{#x|'human'}}; {{#v|@item}}.push({{#x|'camel'}}, {{#x|'moose'}}); {{#cm|# append elements}} {{#v|@item}} = ({{#v|@item}}, {{#x|'camel'}}, {{#x|'moose'}}); {{#cm|# just the same}} ---- {{#cm|# use it as a stack (FILO):}} {{#v|@item}}.push({{#x|'moose'}}); push {{#v|@item}}, {{#x|'elk'}}; {{#cm|# just another way}} {{#v|$top}} = {{#v|@item}}[-1]; {{#v|$top}} = {{#v|@item}}.pop(); {{#v|$top}} = {{#v|@item}}.pop; {{#cm|# ditto}} ---- {{#cm|# use it as a queue (FIFO):}} {{#v|@item}}.unshift({{#x|256}}); unshift {{#v|@item}}, {{#x|128}}, {{#x|'hello'}}; {{#v|$elem}} = {{#v|@item}}.shift(); {{#v|$elem}} = {{#v|@item}}.shift; {{#v|$elem}} = shift {{#v|@item}}; say {{#x|"length of the queue: "}}, {{#v|@elem}}.elems; ---- Make {{#x|simple}} things {{#ci|easy}} and {{#x|hard}} things {{#ci|possible}}. -- Larry Wall 让简单的事情很容易办到， 让困难的事情有可能办到。 ---- Writing a string to a {{#x|file}} should be a {{#ci|simple}} task, however... 向一个文件写入一个字符串本该是 一件很简单的任务，可是…… ---- {{#cm|# The Java way:}} {{#kw|import}} java.io.*; {{#kw|class}} WriteFile { {{#kw|public static void}} main(String args[]) { FileOutputStream foStream; PrintStream pStream; {{#kw|try}} { foStream = {{#kw|new}} FileOutputStream({{#x|"somefile.txt"}}); pStream = {{#kw|new}} PrintStream( foStream ); pStream.println ({{#x|"This is written to a file"}}); pStream.close(); } {{#kw|catch}} (Exception e) { System.err.println ({{#x|"Error writing to file "}} + e); } } } ---- {{#cm|/* The C way: */}} {{#kw|#include}} <stdio.h> {{#kw|#include}} <stdlib.h> {{#kw|int}} main() { FILE* fh; {{#kw|if}} ((fh = fopen({{#x|"somefile.txt"}}, {{#x|"w"}}) == NULL) { fprintf(stderr, {{#x|"Can't open file: %s"}}, strerror(errno)); return 1; } fprintf(fh, {{#x|"This is written to a file\\n"}}); fclose(fh); return {{#x|0}}; } ---- {{#cm|# The Perl 5 way:}} open {{#kw|my}} {{#v|$fh}}, {{#x|"> somefile.txt"}} {{#kw|or}} die {{#x|"Can't open file: $!"}}; print {{#v|$fh}} {{#x|"This is written to a file\\n"}} {{#kw|or}} die {{#x|"Can't print to file: $!"}}; close {{#v|$fh}}; ---- {{#tag|☆}} {{#ci|output arguments}} <=> {{#ci|return values}} 输出参数 {{#cm|<=>}} 返回值 ---- {{#cm|/* pass results via return values */}} {{#kw|int}} add({{#kw|int}} a, {{#kw|int}} b) { {{#kw|return}} a + b; } ... {{#kw|if}} (add({{#x|1}}, {{#x|2}}) == {{#x|3}}) { printf({{#x|"ok"}}); } printf({{#x|"%d"}}, add({{#x|5}}, {{#x|6}})); ---- {{#cm|/* pass results via output arguments */}} {{#kw|void}} add({{#kw|int}} a, {{#kw|int}} b, {{#kw|int}}& c) { c = a + b; } ... {{#kw|int}} temp; add({{#x|1}}, {{#x|2}}, temp); {{#kw|if}} (temp == {{#x|3}}) { printf({{#x|"ok"}}); } add({{#x|5}}, {{#x|6}}, temp); printf({{#x|"%d"}}, temp); ---- {{#tag|☆}} {{#ci|Multiple}} return values 多重返回值 ---- {{#cm|# The Perl 6 way:}} {{#kw|sub}} div ({{#v|$a}}, {{#v|$b}}) { {{#kw|return}} ({{#v|$a}}/{{#v|$b}}, {{#v|$a}}%{{#v|$b}}); } ... {{#kw|my}} ({{#v|$quo}}, {{#v|$rem}}) = div({{#x|5}}, {{#x|2}}); ---- {{#cm|/* The C way: */}} {{#kw|void}} div ({{#kw|int}} a, {{#kw|int}} b, {{#kw|int}}* ptr_quo, {{#kw|int}}* ptr_rem) { *ptr_quo = a / b, *ptr_rem = a % b; } ... {{#kw|int}} quo, rem; div(5, 2, &quo, &rem); ---- {{#cm|// The C++ way:}} {{#kw|void}} div ({{#kw|int}} a, {{#kw|int}} b, {{#kw|int}}& quo, {{#kw|int}}& rem) { quo = a / b; rem = a % b; } ... {{#kw|int}} quo, rem; div(5, 2, quo, rem); ---- {{#tag|☆}} The {{#ci|power}} of {{#x|notation}} 记法的威力 ---- {{#ci|Inventing}} a language doesn't necessarily mean building the successor to Java; often a thorny problem can be {{#ci|cleared}} up by a change of {{#x|notation}}... -- \"The Practice of Programming\" 发明一种语言并不一定意味着创建 Java 的继承者；通 常一个很棘手的问题可以通过记法上的改变而获得澄清。 -- 《程序设计实践》 ---- {{#cm|Case #1}}: {{#x|Formated}} output 案例 #1: 格式化输出 ---- {{#cm|// The C++ style:}} cout << {{#x|"{ list["}} << i << {{#x|"]["}} << j << {{#x|"] = "}} << elems[i][j] << {{#x|" }\\n"}}; +{{#x|☹}} This is {{#ci|ugly}}. ---- {{#cm|// The C style:}} printf({{#x|"{ list[%d][%d] = %f }\\n"}}, i, j, elems[i][j]); +{{#x|☺}} This is {{#ci|much better}}. ---- The problem is that many developers choose the solution {{#ci|before}} defining the problem. It's {{#x|not}} the case that any programming language is {{#x|"one size fits all"}}. -- Ovid 问题就在于许多开发人员在定义问题之前就选定了解 决方案。并不存在一种编程语言能做到“一劳永逸”。 ---- {{#cm|Case #2}}: A simple-minded {{#x|CSV}} file {{#ci|parser}} in {{#x|Perl 6}} 案例 #2: 一个简单的逗号分隔(CSV)文件的解析器 （使用 Perl 6） ---- {{#kw|my}} {{#v|$csv_src}} = slurp {{#v|$csv_file}}; {{#kw|my}} {{#v|@lines}} = split {{#x|/[\\n\\s]+/}}, {{#v|$csv_src}}; {{#kw|for}} {{#v|@lines}} -> {{#v|$line}} { {{#kw|my}} {{#v|@fields}} = split {{#x|/\\s*,\\s*/}}, {{#v|$line}}; {{#cm|# process the fields here...}} } ---- {{#x|☺}} Job {{#ci|done}}! {{#cm|♨}} ---- In {{#x|large}} applications covering problem domains suitable for {{#ci|both}} {{#x|Perl}} and {{#x|Java}}, the Java programmer {{#ci|can't}} hold a candle to me. -- Ovid 对于 Perl 和 Java 都适合的大型应用， Java 程序员根本无法赶上我的编程效率。 ---- {{#tag|☆}} {{#ci|Higher}} order functions ({{#x|λ}} calculus) 高阶函数（λ 演算） ---- C# {{#x|3.0}} (“C# Orcas”) introduces several language extensions that build on C# 2.0 to support the creation and use of {{#ci|higher order}}, {{#x|functional}} style class libraries. The extensions enable construction of {{#ci|compositional}} APIs that have equal {{#ci|expressive power}} of query languages in domains such as relational databases and XML. -- C# Version 3.0 Specification ---- Closures ➥ A piece of {{#x|code}} {{#ci|manipulable}} in {{#ci|arbitrary}} contexts ---- {{#kw|my}} {{#v|$foo}} = { say {{#x|1}} + {{#x|2}} }; {{#kw|my}} {{#v|$bar}} = {{#v|$foo}}; {{#v|$bar}}.(); {{#cm|# prints 3}} {{#v|$foo}}.(); {{#cm|# ditto }} ---- {{#x|☺}} Closures can {{#ci|remember}} the {{#x|context}} in which it was created. ---- {{#kw|sub}} factory({{#v|$seed}}) { {{#kw|return}} { say {{#v|$seed}} }; } {{#kw|my}} {{#v|$foo}} = factory({{#x|7}}); {{#v|$foo}}.(); {{#cm|# prints 7}} {{#kw|my}} {{#v|$bar}} = factory({{#x|100}}); {{#v|$bar}}.(); {{#cm|# prints 100}} {{#v|$foo}}.(); {{#cm|# still prints 7}} ---- {{#x|Higher order}} functions ➥ 0 {{#ci|loops}} 高阶函数 ➥ 0 循环 ---- {{#cm|Case #1}}: We want to print out {{#ci|all}} the elements contained in an {{#x|array}} of {{#x|arrays}}. 案例 #1： 我们想打印出一个 数组的数组里的所有元素。 ---- {{#cm|// The C# way (using loops):}} {{#kw|int}}[][] elems = {{#kw|new int}}[][] { {{#kw|new int}}[] {1,2}, {{#kw|new int}}[] {3,4,5} }; {{#kw|for}} ({{#kw|int}} i = 0; i < elems.length; i++) {{#kw|for}} ({{#kw|int}} j = 0; j < elems[i].length; j++) Console.WriteLine(elems[i][j]); ---- {{#cm|# The Perl 6 way:}} {{#kw|my}} {{#v|@elems}} = [1,2], [3,4,5]; map { map { .say }, {{#v|$\_}} }, {{#v|@elems}}; ---- {{#cm|# Anyway, we can still use loops in Perl 6:}} {{#kw|my}} {{#v|@elems}} = [1,2], [3,4,5]; {{#kw|for}} {{#v|@elems}} { {{#kw|for}} {{#v|\@\$\_}} { .say } } ---- {{#cm|Case #2}}: We want to {{#ci|filter}} out customers with {{#x|income}} higher than $ 5000. 案例 #2: 我们想到筛选出所有收入在 5000 美 元以上的客户 ---- {{#cm|# Traditional way in Perl 6 (using loops):}} {{#kw|my}} {{#v|@res}}; {{#kw|for}} {{#v|@customers}} -> {{#v|$customer}} { {{#kw|if}} {{#v|$customer}}.income() > {{#x|5000}} { push {{#v|@res}}, {{#v|$customer}}; } } ---- {{#cm|# As before, but more concise:}} {{#kw|my}} {{#v|@res}}; {{#kw|for}} {{#v|@customers}} { {{#kw|if}} .income > {{#x|5000}} { push {{#v|@res}}, {{#v|$\_}}; } } ---- {{#cm|# A functional-style solution:}} {{#kw|my}} {{#v|@res}} = grep { .income > {{#x|5000}} }, {{#v|@customers}}; ---- {{#x|Higher order}} functions ➥ As {{#ci|expressive}} as SQL 高阶函数 ➥ 拥有和 SQL 一样的表达力 ---- {{#cm|Case #1}}: Customer {{#x|filtering}} and {{#x|sorting}} 案例 #1: 客户筛选与排序 ---- {{#kw|select}} * {{#kw|from}} customers {{#kw|where}} income > 5000 {{#kw|and}} gender = {{#x|'female'}} {{#kw|order by}} name ---- {{#kw|my}} {{#v|@res}} = sort { {{#v|$^a}}.name {{#kw|cmp}} {{#v|$^b}}.name }, grep { .income > {{#x|5000}} {{#kw|and}} .gender {{#kw|eq}} {{#x|'female'}} }, {{#v|@customers}}; ---- {{#cm|Case #2}}: Boy student {{#ci|statistics}} 案例 #2: 男生统计信息 ---- {{#kw|select}} class_id, {{#kw|count}}(*) {{#kw|as}} count {{#kw|from}} students {{#kw|where}} gender = {{#x|'male'}} {{#kw|group by}} class_id {{#kw|order by}} count {{#kw|desc}} ---- {{#kw|my}} {{#v|%class}}; map { {{#v|%class}}{.class_id}++ }, grep { .gender {{#kw|eq}} {{#x|'male'}} }, {{#v|@student}}; {{#kw|my}} {{#v|@res}} = reverse sort { {{#v|$^a}}.value {{#kw|<=>}} {{#v|$^b}}.value }, {{#v|%class}}.pairs; ---- {{#x|JIT}} slide making... 即时幻灯片制做…… ---- {{img src="#" width="0" height="0"}} {{img src="images/lastminute.png" width="361" height="455"}} ---- {{#c|Thank you!}} ☺