history | 易学教程

What is “pass-by-name” and how does it work exactly?

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问题 I've checked Wikipedia and googled but I still can't wrap my mind around how pass-by-name works in ALGOL 60. 回答1: I found a good explanation at Pass-By-Name Parameter Passing. Essentially, the body of a function is interpreted at call time after textually substituting the actual parameters into the function body. In this sense the evaluation method is similar to that of C preprocessor macros. By substituting the actual parameters into the function body, the function body can both read and

Where does 'Hello world' come from?

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问题 ' hello, world ' is usually the first example for any programming language. I've always wondered where this sentence came from and where was it first used. I've once been told that it was the first sentence ever to be displayed on a computer screen, but I've not been able to find any reference to this. So my question is: Where does the practice to use ' hello, world ' as the first example for computer languages originate from? Where was it first used? Update Although the answers are quite

Line endings messed up in Git - how to track changes from another branch after a huge line ending fix?

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问题 We are working with a 3rd party PHP engine that gets regular updates. The releases are kept on a separate branch in git, and our fork is the master branch. This way we'll be able to apply patches to our fork from the new releases of the engine. My problem is, after many commits to our branch, I realized that the initial import of the engine was done with CRLF line endings. I converted every file to LF, but this made a huge commit, with 100k lines removed and 100k lines added, which obviously

How could I change window's location without reloading and # hack?

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问题 At first I thought that hash hack is a requirement, however judging from the recent updates from facebook, I am thinking otherwise. The original hash hack (I am not sure if this is the correct term) is that by changing location.hash, one may save a state in the URL without refreshing the page. That is extensively used by Google's apps, and Facebook, and lately #NewTwitter. However today I noticed that Facebook no longer have this "#" if you use a "modern" browser - like chrome or firefox. I

Why are “control” characters illegal in XML 1.0?

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There are a variety of characters that are not legally encodeable in XML 1.0, e.g. U+0007 ('bell') and U+001B ('escape'). Most of the interesting ones are non-whitespace 'control' characters. It's clear from (e.g.) this question and others that it's the XML spec that's the issue -- but can anyone illuminate me as to why the XML spec forbids these characters? It seems like it could have been required that they be encoded in escapes, e.g. as  and  respectively, but perhaps there's a practical reason that the characters were forbidden rather than required to be escaped? Answerers

Can I prevent history.popstate from triggering on initial page-load?

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问题 I\'m working on a site that serves content via AJAX. If you click an item in the menu, a content div gets updated with $.get response, nothing fancy. I\'m implementing history.pushState to allow navigation with the browser\'s back/forward button. I have the following to load content on history navigation: $(function() { $(window).bind(\"popstate\", function() { $.getScript(location.href); }); }); The problem is, when a page is loaded for the first time, this function does $.getScript so the

Why do stacks typically grow downwards?

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I know that in the architectures I'm personally familiar with (x86, 6502, etc), the stack typically grows downwards (i.e. every item pushed onto the stack results in a decremented SP, not an incremented one). I'm wondering about the historical rationale for this. I know that in a unified address space, it's convenient to start the stack on the opposite end of the data segment (say) so there's only a problem if the two sides collide in the middle. But why does the stack traditionally get the top part? Especially given how this is the opposite of the "conceptual" model? (And note that in the

Can tags be automatically moved after a git filter-branch and rebase?

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问题 edit The question boils down to \"Can git rebase be instructed to rebase tags, too?\" But an answer to the original question would also help. Asking How to prepend the past to a git repository? I followed these instructions. < edit >Then I rebased to include a file that was only in the snapshots, see here.< /edit > Since history was rewritten (by git filter-branch or git rebase or both?) all tags are still on the original time line* and I\'d somehow like to move them to the new one. I think I

修改history记录数

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在linux系统下、history命令会保存多少条命令呢？曾在一本书上说，如果注销系统，那么会将所有的历史命令都定入到~/.bash_history, 但只保留1000条命令（这个是由默认的shell变量所设置了的）但是为什么我们执行history命令后会出现大于1000条的历史记录呢，其实当我们仔细一看只是序列大于1000、记录的条数还是1000条。在此我是这样理解的： 1、~/.bash_histroy里面是记录的上次注销前的历史记录（最大保存1000条，且是上次注销前最近的1000条记录） 2、执行history命令，会显示~/.bash_history里的记录加上当前shell所执行记录。且也是只显示1000条记录、如重新登录后、执行ls命令后、再使用history查看、会显示.bash_history里的+ls和history这两条。如果~/.bash_history里有1000条、则显示后 998+ls 和 history 这两条命令。 3、我们可以修改history的历史保留命令的条数；可以查看history的默认保留条数 echo $HISTSIZE 一般默认是1000条如下图所示：如果为了安全我们只需要保留200条，怎么办呢？我们可以临时修改最大保留条数： HISTSIZE=200 这样就修改成了200条啦，但是重启服务器后，又还原了。

How can I rewrite history so that all files, except the ones I already moved, are in a subdirectory?

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问题 I have a project under git . One day I moved all project files from current directory to foo/bar/ under the project. I did it using git mv . Then I added some more files and did some changes to already existing files. As a result, now when I look at the history of foo/bar/file.c , I can only see changes that I did after I moved the file. I tried to fix this in various ways ( filter-branch with subdirectory filter, etc), but nothing helped, so I am pretty stacked here. I\'ll appreciate any