According to the class file format used by the JVM, may a field or method legally have the empty string as its "unqualified name"? The only real restriction I can find in the relevant section is:
An unqualified name must not contain any of the ASCII characters . ; [ / (that is, period or semicolon or left square bracket or forward slash).
But I'm still having trouble believing this wouldn't cause issues somewhere else. Is the empty string really valid as a field/method name?
NO. JVMS SE 8 §4.2.2:
An unqualified name must contain at least one Unicode code point
JVMS SE 7 did not have this note.
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Is there any language that allows spaces in its variable names [closed]
(2 answers)
Closed 9 years ago.
Related: Why can't variable names start with numbers?
Is there a technical reason why spaces aren't allowed in variable names or is it down to convention?
For example, what's stopping us from doing something like this?:
average score = sum of scores / number of scores
The only issue that comes to mind is keywords, but one could simply restrict the use of them in a variable name, and the lexer would be able to distinguish between part of a variable and a keyword.
There’s no fundamental reason, apart from the decisions of language designers and a history of single-token identifiers. Some languages in fact do allow multi-token identifiers: MultiMedia Fusion’s expression language, some Mac spreadsheet/notebook software whose name escapes me, and I’m sure of others. There are several considerations that make the problem nontrivial, though.
Presuming the language is free-form, you need a canonical representation, so that an identifier like account name is treated the same regardless of whitespace. A compiler would probably need to use some mangling convention to please a linker. Then you have to consider the effect of that on foreign exports—why C++ has the extern "C" linkage specifier to disable mangling.
Keywords are an issue, as you have seen. Most C-family languages have a lexical class of keywords distinct from identifiers, which are not context-sensitive. You cannot name a variable class in C++. This can be solved by disallowing keywords in multi-token identifiers:
if account age < 13 then child account = true;
Here, if and then cannot be part of an identifier, so there is no ambiguity with account age and child account. Alternatively, you can require punctuation everywhere:
if (account age < 13) {
child account = true;
}
The last option is to make keywords pervasively context-sensitive, leading to such monstrosities as:
IF IF = THEN THEN ELSE = THEN ELSE THEN = ELSE
The biggest issue is that juxtaposition is an extremely powerful syntactic construct, and you don’t want to occupy it lightly. Allowing multi-token identifiers prevents using juxtaposition for another purpose, such as function application or composition. Far better, I think, just to allow most nonwhitespace characters and thereby permit such identifiers as canonical-venomous-frobnicator. Still plenty readable but with fewer opportunities for ambiguity.
I think it is bacause the designers of the language have followed this convention.
I have searched on Google and found that while naming a variable this is a rule which is followed while naming a variable.
Some links are given below:-
SPSS notes
The following rules apply to variable names:
Variable names cannot contain spaces.
C Programming/Variables
Variable names by IBM
Java Variable Naming convention
Variable names are case-sensitive. A variable's name can be any legal
identifier — an unlimited-length sequence of Unicode letters and
digits, beginning with a letter, the dollar sign "$", or the
underscore character "". The convention, however, is to always begin
your variable names with a letter, not "$" or "". Additionally, the
dollar sign character, by convention, is never used at all. You may
find some situations where auto-generated names will contain the
dollar sign, but your variable names should always avoid using it. A
similar convention exists for the underscore character; while it's
technically legal to begin your variable's name with "_", this
practice is discouraged. White space is not permitted.
Wiki for Naming Convention
In all of the above links you will find that the designers have followed this naming convention for naming the variable.
Also check Is there any language that allows spaces in its variable names
This is forced from language designing.
Compiler needs to find out the meaning of words.
Compiler works on a "State Machine" method, and it needs to distinguish key words.
Maybe placing variable names in "[" and "]" give us some solution(like SQL).
But it will be harder to use it in coding...
Let's say, I have a regular expression that checks the validation of the input value as a whole. For example, it is an email input box and when user hits enter, I check it against ^[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}$ to see if it is a valid email address.
What I want to achieve is, I want to intercept the character input too, and check every single input character to see if that character is also a valid character. I can do this by adding an extra regular expression, e.g. [A-Z0-9._%+-] but that is not what I want.
Is there a way to extract the widest possible range of acceptable characters from a given regular expression? So in the example above, can I extract all the valid characters that are defined by the original regular expression (i.e. ^[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,4}$) programmatically?
I would appreciate any help or hint.
P.S. This is project for iOS written in Objective-C.
If you don't mind writing half a regex parser, certainly. You would have to be able to distinguish literals from meta-characters and to unroll/merge all character classes (including negated character classes, and nested negated character classes, if you regex flavor supports them).
If NSRegularExpressions doesn't come with some convenience method, I cannot imagine how it would be possible otherwise. Just think about ^. When it is outside of a character class, it's a meta-character that you can ignore. If it is inside a character class, it's a meta-character, that negates the character class unless it is not the first character. - is a meta-character inside character classes, unless it is the first character, the last character, or right after another character range (depending on regex flavor). And I'm not even speaking about escaped characters.
I don't know about NSRegularExpressions, but some flavors also support nested character classes (like [a-z[^aeiou]] for all consonants). I think you get where I am going with this.
I recently read some of : https://www.rfc-editor.org/rfc/rfc6570#section-1
And I found the following URL template examples :
GIVEN :
var="value";
x=1024;
path=/foo/bar;
{/var,x}/here /value/1024/here
{#path,x}/here #/foo/bar,1024/here
These seem contradictory.
In the first one, it appears that the / replaces ,
In the 2nd one, it appears that the , is kept .
Thus, I'm wondering wether there are inconsistencies in this particular RFC. I'm new to these RFC's so maybe I don't fully understand the culture behind how these develop.
There's no contradiction in those two examples. They illustrate the point that the rules for expanding an expression whose first character is / are different from the rules for expanding an expression whose first character is #. These alternative expansion rules are pretty much the entire point of having a variety of different magic leading characters -- which are called operators in the RFC.
The expression with the leading / is expanded according to a rule that says "each variable in the expression is replaced by its value, preceded by a / character". (I'm paraphrasing the real rule, which is described in section 3.2.6 of that RFC.) The expression with the leading # is expanded according to a rule that says "each variable in the expression is replaced by its value, with the first variable preceded by a # and subsequent variables preceded by a ,. (Again paraphrased, see section 3.2.4 for the real rule.)
I'd like to create a regular expression such that when I compare the a string against an array of strings, matches are returned with the regex ignoring certain characters.
Here's one example. Consider the following array of names:
{
"Andy O'Brien",
"Bob O'Brian",
"Jim OBrien",
"Larry Oberlin"
}
If a user enters "ob", I'd like the app to apply a regex predicate to the array and all of the names in the above array would match (e.g. the ' is ignored).
I know I can run the match twice, first against each name and second against each name with the ignored chars stripped from the string. I'd rather this by done by a single regex so I don't need two passes.
Is this possible? This is for an iOS app and I'm using NSPredicate.
EDIT: clarification on use
From the initial answers I realized I wasn't clear. The example above is a specific one. I need a general solution where the array of names is a large array with diverse names and the string I am matching against is entered by the user. So I can't hard code the regex like [o]'?[b].
Also, I know how to do case-insensitive searches so don't need the answer to focus on that. Just need a solution to ignore the chars I don't want to match against.
Since you have discarded all the answers showing the ways it can be done, you are left with the answer:
NO, this cannot be done. Regex does not have an option to 'ignore' characters. Your only options are to modify the regex to match them, or to do a pass on your source text to get rid of the characters you want to ignore and then match against that. (Of course, then you may have the problem of correlating your 'cleaned' text with the actual source text.)
If I understand correctly, you want a way to match the characters "ob" 1) regardless of capitalization, and 2) regardless of whether there is an apostrophe in between them. That should be easy enough.
1) Use a case-insensitivity modifier, or use a regexp that specifies that the capital and lowercase version of the letter are both acceptable: [Oo][Bb]
2) Use the ? modifier to indicate that a character may be present either one or zero times. o'?b will match both "o'b" and "ob". If you want to include other characters that may or may not be present, you can group them with the apostrophe. For example, o['-~]?b will match "ob", "o'b", "o-b", and "o~b".
So the complete answer would be [Oo]'?[Bb].
Update: The OP asked for a solution that would cause the given character to be ignored in an arbitrary search string. You can do this by inserting '? after every character of the search string. For example, if you were given the search string oleary, you'd transform it into o'?l'?e'?a'?r'?y'?. Foolproof, though probably not optimal for performance. Note that this would match "o'leary" but also "o'lea'r'y'" if that's a concern.
In this particular case, just throw the set of characters into the middle of the regex as optional. This works specifically because you have only two characters in your match string, otherwise the regex might get a bit verbose. For example, match case-insensitive against:
o[']*b
You can add more characters to that character class in the middle to ignore them. Note that the * matches any number of characters (so O'''Brien will match) - for a single instance, change to ?:
o[']?b
You can make particular characters optional with a question mark, which means that it will match whether they're there or not, e.g:
/o\'?b/
Would match all of the above, add .+ to either side to match all other characters, and a space to denote the start of the surname:
/.+? o\'?b.+/
And use the case-insensitivity modifier to make it match regardless of capitalisation.
I set the culture to Hungarian language, and Chr() seems to be broken.
System.Threading.Thread.CurrentThread.CurrentCulture = "hu-US"
System.Threading.Thread.CurrentThread.CurrentUICulture = "hu-US"
Chr(254)
This returns "ţ" when it should be "þ"
However, Asc("ţ") returns 116.
This: Asc(Chr(254)) returns 116.
Why would Asc() and Chr() be different?
I checked and the 'wide' functions do work correctly: ascw(chrw(254)) = 254
Chr(254) interprets the argument in a system dependent way, by looking at the System.Globalization.CultureInfo.CurrentCulture.TextInfo.ANSICodePage property. See the MSDN article about Chr. You can check whether that value is what you expect. "hu-US" (the hungarian locale as used in the US) might do something strange there.
As a side-note, Asc() has no promise about the used codepage in its current documentation (it was there until 3.0).
Generally I would stick to the unicode variants (ending on -W) if at all possible or use the Encoding class to explicitly specify the conversions.
My best guess is that your Windows tries to represent Chr(254)="ţ" as a combined letter, where the first letter is Chr(116)="t" and the second ("¸" or something like that) cannot be returned because Chr() only returns one letter.
Unicode text should not be handled character-by-character.
It sounds like you need to set the code page for the current thread -- the current culture shouldn't have any effect on Asc and Chr.
Both the Chr docs and the Asc docs have this line:
The returned character depends on the code page for the current thread, which is contained in the ANSICodePage property of the TextInfo class. TextInfo.ANSICodePage can be obtained by specifying System.Globalization.CultureInfo.CurrentCulture.TextInfo.ANSICodePage.
I have seen several problems in VBA on the Mac where characters over 127 and some control characters are not treated properly.
This includes paragraph marks (especially in text copied from the internet or scanned), "¥", and "Ω".
They cannot always be searched for, cannot be used in file names - though they could in the past, and when tested, come up as another ascii number. I have had to write algorithms to change these when files open, as they often look like they are the right character, but then crash some of my macros when they act strangely. The character will look and act right when I save the file, but may be changed when it is reopened.
I will eventually try to switch to unicode, but I am not sure if that will help this issue.
This may not be the issue that you are observing, but I would not rule out isolated problems with certain characters like this. I have sent notes to MS about this in the past but have received no joy.
If you cannot find another solution and the character looks correct when you type it in, then I recommend using a macro snippet like the one below, which I run when updating tables. You of course have to setup theRange as the area you are looking at. A whole file can take a while.
For aChar = 1 To theRange.Characters.count
theRange.Characters(aChar).Select
If Asc(Selection.Text) = 95 And Selection.Text <> "_" Then Selection.TypeText "Ω"
Next aChar