hostname: use missing

Author: scivision

+stdlib/+dotnet/hostname.m

@@ -9,7 +9,7 @@
   n = char(System.Net.Dns.GetHostName());
 catch e
   dotnetException(e);
-  n = '';
+  n = missing;
 end
 
 % https://learn.microsoft.com/en-us/dotnet/api/system.net.dns.gethostname

+stdlib/+java/hostname.m

@@ -4,7 +4,7 @@
   n = char(java.net.InetAddress.getLocalHost().getHostName());
 catch e
   javaException(e);
-  n = '';
+  n = missing;
 end
 
 end

+stdlib/+python/hostname.m

@@ -4,7 +4,7 @@
   n = char(py.socket.gethostname());
 catch e
   pythonException(e)
-  n = '';
+  n = missing;
 end
 
 end

+stdlib/+shell/hostname.m

@@ -1,12 +1,12 @@
 function [n, cmd] = hostname()
 
+n = missing;
+
 cmd = 'hostname';
-[s, n] = system(cmd);
+[s, r] = system(cmd);
 
 if s == 0
-  n = deblank(n);
-else
-  n = '';
+  n = deblank(r);
 end
 
 end

+stdlib/hostname.m

@@ -13,7 +13,7 @@
   backend (1,:) string = ["java", "dotnet", "python", "shell"]
 end
 
-r = '';
+r = missing;
 
 for b = backend
   switch b
@@ -31,7 +31,7 @@
       error('stdlib:hostname:ValueError', 'Unknown backend: %s', b)
   end
 
-  if ~isempty(r)
+  if ~ismissing(r)
     return
   end
 end

test/TestBackend.m

@@ -84,7 +84,7 @@ function test_backend(tc)
 
 [i, b] = stdlib.hostname();
 tc.assertThat(b, IsSubsetOf(stdlib.Backend('hostname').backends))
-tc.verifyNotEmpty(i)
+tc.verifyClass(i, 'char')
 
 [i, b] = stdlib.inode(readme);
 tc.assertThat(b, IsSubsetOf(stdlib.Backend('inode').backends))

test/TestSys.m

@@ -78,12 +78,12 @@ function test_checkRAM(tc)
 function test_hostname(tc, B_jdps)
 [h, b] = stdlib.hostname(B_jdps);
 tc.assertMatches(b, B_jdps)
-tc.verifyClass(h, 'char')
 
 if ismember(B_jdps, stdlib.Backend().select('hostname'))
+  tc.verifyClass(h, 'char')
   tc.verifyGreaterThan(strlength(h), 0)
 else
-  tc.verifyEmpty(h)
+  tc.verifyEqual(h, missing)
 end
 end