How to use tolower in D

Question

I want to to put the first letter of a string into lowercase in D.

As a string is imutable in D, there doesn't seem to be a simple way.

I came up with this:

string mystr = "BookRef";
string outval = toLower( mystr[0..1] ) ~ mystr[1..$]; 
writeln( "my outval: ", outval );

Is there an easier way ?

greenify · Answer 1 · 2019-04-30T20:12:17.697

6

For reference and completeness, you can build this without any allocations by chaining ranges. It has the additional advantages of working with empty strings:

auto downcase(string w)
{
    import std.range, std.uni;
    return w.take(1).asLowerCase.chain(w.drop(1));
}

Try online on run.dlang.io.

edited Apr 30 '19 at 20:12

answered Apr 03 '19 at 10:07

greenify

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I've tried this but it doesn't work with empty strings. https://run.dlang.io/is/ksDBNT. – Patrick Apr 30 '19 at 11:41
1

Sorry, `dropOne` enforces that the element is actually there, which is why it didn't work with empty strings. Updated the code to use `drop(1)` which essentially does nothing with empty strings. – greenify Apr 30 '19 at 20:13

score 2 · Accepted Answer · answered Apr 03 '19 at 09:05

2

While D strings are immutable, you can use char[] instead:

char[] mystr = "BookRef".dup; // .dup to create a copy
mystr[0] = toLower(mystr[0..1])[0];
writeln("my outval: ", mystr);

answered Apr 03 '19 at 09:05

BioTronic

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What would be intuitive? (So that we can suggest to the D devs) – DejanLekic May 03 '19 at 17:04

How to use tolower in D

2 Answers2