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[perl #132301] a built-in startswith($string, $prefix) function

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From:
l . mai @ web . de
Date:
October 14, 2017 14:19
Subject:
[perl #132301] a built-in startswith($string, $prefix) function
Message ID:
rt-4.0.24-14446-1507990731-741.132301-75-0@perl.org
# New Ticket Created by  l.mai@web.de 
# Please include the string:  [perl #132301]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132301 >



This is a bug report for perl from l.mai@web.de,
generated with the help of perlbug 1.40 running under perl 5.26.0.


-----------------------------------------------------------------
[Please describe your issue here]

Currently Perl has no good way to check whether a string starts with another
string. Current alternatives:

- index($string, $prefix) == 0

  Inefficient because it has to search the whole (potentially large) $string,
  just to see whether the offset was 0.

- $string =~ /^\Q$prefix/

  Inefficient because it has to pass the whole $prefix through quotemeta, then
  compile it to a regex, then do a regex check.

- substr($string, 0, length $prefix) eq $prefix

  I don't know if this actually makes a copy of the beginning of $string, but
  it's awkward: You have to mention $prefix twice, which is annoying if it's a
  more complex expression.

I want to be able to express my intent (check prefixes) directly. As a bonus,
it can easily be implemented to be more efficient than string search / regex
stuff.

That's why I think it would be nice to have

  startswith($string, $prefix)

in core (and maybe endswith($x, $y)).

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=wishlist
---
Site configuration information for perl 5.26.0:

Configured by mauke at Fri Sep 22 13:28:36 CEST 2017.

Summary of my perl5 (revision 5 version 26 subversion 0) configuration:
   
  Platform:
    osname=linux
    osvers=4.9.41-1-lts
    archname=i686-linux
    uname='linux simplicio 4.9.41-1-lts #1 smp mon aug 7 17:57:02 cest 2017 i686 gnulinux '
    config_args=''
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=undef
    use64bitall=undef
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
    bincompat5005=undef
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    optimize='-O2 -march=native'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='7.2.0'
    gccosandvers=''
    intsize=4
    longsize=4
    ptrsize=4
    doublesize=8
    byteorder=1234
    doublekind=3
    d_longlong=define
    longlongsize=8
    d_longdbl=define
    longdblsize=12
    longdblkind=3
    ivtype='long'
    ivsize=4
    nvtype='double'
    nvsize=8
    Off_t='off_t'
    lseeksize=8
    alignbytes=4
    prototype=define
  Linker and Libraries:
    ld='cc'
    ldflags ='-fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/i686-pc-linux-gnu/7.2.0/include-fixed /usr/lib /lib
    libs=-lpthread -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.26.so
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.26'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -march=native -L/usr/local/lib -fstack-protector-strong'


---
@INC for perl 5.26.0:
    /home/mauke/usr/lib/perl5/site_perl/5.26.0/i686-linux
    /home/mauke/usr/lib/perl5/site_perl/5.26.0
    /home/mauke/usr/lib/perl5/5.26.0/i686-linux
    /home/mauke/usr/lib/perl5/5.26.0

---
Environment for perl 5.26.0:
    HOME=/home/mauke
    LANG=en_US.UTF-8
    LANGUAGE=en_US
    LC_COLLATE=C
    LC_MONETARY=de_DE.UTF-8
    LC_TIME=de_DE.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/mauke/perl5/perlbrew/bin:/home/mauke/bin:/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
    PERLBREW_BASHRC_VERSION=0.73
    PERLBREW_HOME=/home/mauke/.perlbrew
    PERLBREW_ROOT=/home/mauke/perl5/perlbrew
    PERL_BADLANG (unset)
    PERL_UNICODE=SAL
    SHELL=/bin/bash


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