Difference between revisions of "StartsWith and IsStartOf (String functions)"

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{{Template:String:IsStartOf subtitle}}
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{{Template:String:StartsWith and IsStartOf subtitle}}
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<var>StartsWith</var> can be conveniently used to check whether one string starts with another string; <var>IsStartOf</var> can be conveniently used to check whether a string is an abbreviation of a known string.
 
   
 
   
 
==Syntax==
 
==Syntax==
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{{Template:String:StartsWith syntax}}
 
{{Template:String:IsStartOf syntax}}
 
{{Template:String:IsStartOf syntax}}
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===Syntax terms===
 
===Syntax terms===
 
<table class="syntaxTable">
 
<table class="syntaxTable">
 
<tr><th>%boolean</th>
 
<tr><th>%boolean</th>
<td>The <var>Boolean</var> result of <var>IsStartOf</var> is <var>True</var> if:<ul><li>The length of the method object <var class="term">string</var> is at least the value of the <var>MinLength</var> argument<br><b>and</b>:<li>the method object <var class="term">string</var> is the same as the initial substring, whose length is the length of <var class="term">string</var>, of the <var class="term">longerString</var> argument.</ul>If either of the above conditions does not hold, the result is <var>False</var>.</td></tr>
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<td>The <var>[[Boolean enumeration|Boolean]]</var> result is <var>True</var> if <var class="term">abbreviation</var> is the same as the initial substring, whose length is the length of <var class="term">abbreviation</var>, of <var class="term">longerString</var>.
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In addition, for <var>IsStartOf</var>, the length of the method object <var class="term">abbreviation</var> is at least the value of the <var>MinLength</var> argument.
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</td></tr>
 
<tr><th>string</th>
 
<tr><th>string</th>
<td>A string which is examined to see if it is an abbreviation (i.e., an initial substring) of <var class="term">longerString</var>.</td></tr>
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<td>The method object string.  Depending upon whether the <var>StartsWith</var> or <var>IsStartOf</var> method is being used, <var class="term">string</var> may be either the:
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<ul><li><var class="term">longerString</var>, whose intial characters are examined, for <var>StartsWith</var>
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<li><var class="term">abbreviation</var>, for <var>IsStartOf</var></ul></td></tr>
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<tr><th>abbreviation</th><td>A string which is examined to see if it is an abbreviation (that is, an initial substring) of <var class="term">string</var>.</td></tr>
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<tr><th>longerString</th>
 
<tr><th>longerString</th>
<td>A string which is examined to see if the method object <var class="term">string</var> is an abbreviation of it.</td></tr>
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<td>A string which is examined to see if <var class="term">string</var> is an abbreviation of it.</td></tr>
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<tr><th><var>MinLength</var></th>
 
<tr><th><var>MinLength</var></th>
<td>This name-required argument is a non-negative number, specifying the minimum length of the method object <var class="term">string</var> to be considered an abbreviation of <var class="term">longerString</var>. Note that if this is 0, then the null string is an abbreviation of any value of the <var class="term">longerString</var> argument; if this is non-0, then the null string is never an abbreviation.</td></tr>
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<td>This [[Notation conventions for methods#Named parameters|name required]] argument is a non-negative number, specifying the minimum length of <var class="term">string</var> to be considered an abbreviation of <var class="term">longerString</var>. Note that if this is 0, then the null string is an abbreviation of any value of the <var class="term">longerString</var> argument; if this is non-0, then the null string is never an abbreviation.
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This argument is only used by <var>IsStartOf</var>; for <var>StartsWith</var>, <var>MinLength</var> is effectively 0.
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</td></tr>
 
</table>
 
</table>
  
 
==Examples==
 
==Examples==
===Determining if option is valid abbreviation===
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====Checking whether string starts with some literal====
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Hopefully the following fragment is self-evident:
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<p class="code">if %name:toUpper:startsWith('DAV') then
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  print 'Name is probably Dave or David'
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</p>
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====Determining if option is valid abbreviation====
 
A common task is checking user input for a valid abbreviation for one of several longer terms.  This is one motivation for the <var>MinLength</var> argument; there may be overlap in the initial substrings of the longer terms.  Consider the following fragment:
 
A common task is checking user input for a valid abbreviation for one of several longer terms.  This is one motivation for the <var>MinLength</var> argument; there may be overlap in the initial substrings of the longer terms.  Consider the following fragment:
 
<p class="code">%opt = %(system):[[Arguments (System function)|arguments]]:toUpper
 
<p class="code">%opt = %(system):[[Arguments (System function)|arguments]]:toUpper
Line 27: Line 48:
 
If the argument to this proc is <code>max</code>, that would not distinguish it between <code>maxAmount</code> and <code>maxTime</code>; hence the <var>MinLength</var> argument value of 5 is used to enforce that at least <code>maxAm</code> or <code>maxTi</code> is entered (a value of 4 would also have disambiguated the abbreviations in this case).
 
If the argument to this proc is <code>max</code>, that would not distinguish it between <code>maxAmount</code> and <code>maxTime</code>; hence the <var>MinLength</var> argument value of 5 is used to enforce that at least <code>maxAm</code> or <code>maxTi</code> is entered (a value of 4 would also have disambiguated the abbreviations in this case).
  
===Several single-line examples===
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====Several single-line examples====
 
The following fragment:
 
The following fragment:
<p class="code">PrintText {~= 'a':IsStartOf('abc', 1) }
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<p class="code">PrintText {~= 'a':IsStartOf('abc', MinLength=1) }
PrintText {~= 'a':IsStartOf('abc', 2) }
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PrintText {~= 'a':IsStartOf('abc', MinLength=2) }
PrintText {~= 'a':IsStartOf('abc', 0) }
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PrintText {~= 'a':IsStartOf('abc', MinLength=0) }
PrintText {~= 'x':IsStartOf('abc', 1) }
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PrintText {~= 'x':IsStartOf('abc', MinLength=1) }
PrintText {~= 'x':IsStartOf('abc', 0) }
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PrintText {~= 'x':IsStartOf('abc', MinLength=0) }
PrintText {~= '':IsStartOf('abc', 0) }
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PrintText {~= &#39;':IsStartOf('abc', MinLength=0) }
 
</p>
 
</p>
 
produces the following output:
 
produces the following output:
<p class="output">'a':IsStartOf('abc', 1) = True
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<p class="output">'a':IsStartOf('abc', MinLength=1) = True
'a':IsStartOf('abc', 2) = False
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'a':IsStartOf('abc', MinLength=2) = False
'a':IsStartOf('abc', 0) = True
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'a':IsStartOf('abc', MinLength=0) = True
'x':IsStartOf('abc', 1) = False
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'x':IsStartOf('abc', MinLength=1) = False
'x':IsStartOf('abc', 0) = False
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'x':IsStartOf('abc', MinLength=0) = False
 
</p>
 
</p>
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==See also==
 
==See also==
{{Template:String:IsStartOf footer}}
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{{Template:String:StartsWith and IsStartOf footer}}

Latest revision as of 03:09, 21 February 2020

Is one string an initial substring of a longer string? (String class)

[Introduced in Sirius Mods 7.9]

StartsWith can be conveniently used to check whether one string starts with another string; IsStartOf can be conveniently used to check whether a string is an abbreviation of a known string.

Syntax

%boolean = string:StartsWith( abbreviation)

%boolean = string:IsStartOf( longerString, MinLength= number)

Syntax terms

%boolean The Boolean result is True if abbreviation is the same as the initial substring, whose length is the length of abbreviation, of longerString.

In addition, for IsStartOf, the length of the method object abbreviation is at least the value of the MinLength argument.

string The method object string. Depending upon whether the StartsWith or IsStartOf method is being used, string may be either the:
  • longerString, whose intial characters are examined, for StartsWith
  • abbreviation, for IsStartOf
abbreviationA string which is examined to see if it is an abbreviation (that is, an initial substring) of string.
longerString A string which is examined to see if string is an abbreviation of it.
MinLength This name required argument is a non-negative number, specifying the minimum length of string to be considered an abbreviation of longerString. Note that if this is 0, then the null string is an abbreviation of any value of the longerString argument; if this is non-0, then the null string is never an abbreviation.

This argument is only used by IsStartOf; for StartsWith, MinLength is effectively 0.

Examples

Checking whether string starts with some literal

Hopefully the following fragment is self-evident:

if %name:toUpper:startsWith('DAV') then print 'Name is probably Dave or David'

Determining if option is valid abbreviation

A common task is checking user input for a valid abbreviation for one of several longer terms. This is one motivation for the MinLength argument; there may be overlap in the initial substrings of the longer terms. Consider the following fragment:

%opt = %(system):arguments:toUpper if %opt:isStartOf('MAXAMOUNT', MinLength=5) then ... elseIf %opt:isStartOf('MAXTIME', MinLenth=5) then ... else PrintText Invalid argument: {%opt}

If the argument to this proc is max, that would not distinguish it between maxAmount and maxTime; hence the MinLength argument value of 5 is used to enforce that at least maxAm or maxTi is entered (a value of 4 would also have disambiguated the abbreviations in this case).

Several single-line examples

The following fragment:

PrintText {~= 'a':IsStartOf('abc', MinLength=1) } PrintText {~= 'a':IsStartOf('abc', MinLength=2) } PrintText {~= 'a':IsStartOf('abc', MinLength=0) } PrintText {~= 'x':IsStartOf('abc', MinLength=1) } PrintText {~= 'x':IsStartOf('abc', MinLength=0) } PrintText {~= '':IsStartOf('abc', MinLength=0) }

produces the following output:

'a':IsStartOf('abc', MinLength=1) = True 'a':IsStartOf('abc', MinLength=2) = False 'a':IsStartOf('abc', MinLength=0) = True 'x':IsStartOf('abc', MinLength=1) = False 'x':IsStartOf('abc', MinLength=0) = False

See also