4 files changed, 7 insertions, 11 deletions
diff --git a/acf/model/field.lua b/acf/model/field.lua
index d4e934c..362c7ab 100644
--- a/acf/model/field.lua
+++ b/acf/model/field.lua
@@ -32,9 +32,7 @@ end
 
 function M.Member:auto_ui_name(name)
    if not name then return end
-   return string.gsub(
-      string.upper(string.sub(name, 1, 1))..string.sub(name, 2), '-', ' '
-   )
+   return (name:sub(1, 1):upper()..name:sub(2)):gsub('-', ' ')
 end
 
 function M.Member:meta(context)
@@ -129,7 +127,7 @@ end
 
 function M.String:validate(context, value)
    super(self, M.String):validate(context, value)
-   if self['max-length'] and string.len(value) > self['max-length'] then
+   if self['max-length'] and value:len() > self['max-length'] then
       raise(context.path, 'Maximum length exceeded')
    end
 end
diff --git a/acf/model/init.lua b/acf/model/init.lua
index 9d09204..0254fce 100644
--- a/acf/model/init.lua
+++ b/acf/model/init.lua
@@ -112,7 +112,7 @@ function M.Reference:_validate(context, value)
       if not stringy.startswith(value, prefix) then
 	 raise(path, 'Reference out of scope ('..scope..')')
       end
-      value = string.sub(value, string.len(prefix) + 1, -1)
+      value = value:sub(prefix:len() + 1, -1)
    end
 
    -- assume one-level ref for now
@@ -158,7 +158,7 @@ end
 
 function M.Collection:auto_ui_name(name)
    if not name then return end
-   if string.sub(name, -1, -1) ~= 's' then name = name..'s' end
+   if name:sub(-1, -1) ~= 's' then name = name..'s' end
    return super(self, M.Collection):auto_ui_name(name)
 end
 
diff --git a/acf/model/net.lua b/acf/model/net.lua
index e5c1836..ae82f1e 100644
--- a/acf/model/net.lua
+++ b/acf/model/net.lua
@@ -31,7 +31,7 @@ function M.IPv4Address:validate(context, value)
 	 if tonumber(octet) > 255 then return true end
       end
    end
-   if test(string.match(value, '^(%d+)%.(%d+)%.(%d+)%.(%d+)$')) then
+   if test(value:match('^(%d+)%.(%d+)%.(%d+)%.(%d+)$')) then
       raise(context.path, 'Invalid IPv4 address')
    end
 end
@@ -63,7 +63,7 @@ function M.IPv6Address:validate(context, value)
       if comp == '' then
 	 if short then invalid() end
 	 short = true
-      elseif not string.match(comp, '^%x%x?%x?%x?$') then invalid() end
+      elseif not comp:match('^%x%x?%x?%x?$') then invalid() end
    end
    if (
       short and #comps == 3 and comps[2] == ''
diff --git a/acf/model/node.lua b/acf/model/node.lua
index b708112..0b02e80 100644
--- a/acf/model/node.lua
+++ b/acf/model/node.lua
@@ -162,9 +162,7 @@ function M.Collection:init(context, params)
 
    mt.meta.type = 'collection'
    mt.meta.members = field:meta()
-   mt.meta['ui-member'] = params.ui_member or string.gsub(
-      mt.meta['ui-name'], 's$', ''
-   )
+   mt.meta['ui-member'] = params.ui_member or mt.meta['ui-name']:gsub('s$', '')
 
    function mt.mmeta(name)
       local res = util.copy(mt.meta.members)