fix lifetime bounds and simplify Variable

src/file.rs

@@ -136,13 +136,13 @@ impl ReadOnlyFile {
     }
 
     /// Get a variable from the group
-    pub fn variable<'g>(&'g self, name: &str) -> error::Result<Option<Variable<'g, 'g>>> {
+    pub fn variable<'f>(&'f self, name: &str) -> error::Result<Option<Variable<'f>>> {
         Variable::find_from_name(self.ncid(), name)
     }
     /// Iterate over all variables in a group
     pub fn variables<'f>(
         &'f self,
-    ) -> error::Result<impl Iterator<Item = error::Result<Variable<'f, 'f>>>> {
+    ) -> error::Result<impl Iterator<Item = error::Result<Variable<'f>>>> {
         super::variable::variables_at_ncid(self.ncid())
     }
 
@@ -164,18 +164,18 @@ impl ReadOnlyFile {
         super::dimension::dimension_from_name(self.ncid(), name)
     }
     /// Iterator over all dimensions in the root group
-    pub fn dimensions<'g>(
-        &'g self,
-    ) -> error::Result<impl Iterator<Item = error::Result<Dimension<'g>>>> {
+    pub fn dimensions<'f>(
+        &'f self,
+    ) -> error::Result<impl Iterator<Item = error::Result<Dimension<'f>>>> {
         super::dimension::dimensions_from_location(self.ncid())
     }
 
     /// Get a group
-    pub fn group(&self, name: &str) -> error::Result<Option<Group>> {
+    pub fn group<'f>(&'f self, name: &str) -> error::Result<Option<Group<'f>>> {
         super::group::group_from_name(self.ncid(), name)
     }
     /// Iterator over all subgroups in the root group
-    pub fn groups<'g>(&'g self) -> error::Result<impl Iterator<Item = Group<'g>>> {
+    pub fn groups<'f>(&'f self) -> error::Result<impl Iterator<Item = Group<'f>>> {
         super::group::groups_at_ncid(self.ncid())
     }
 }
@@ -198,17 +198,25 @@ impl MutableFile {
     }
 
     /// Get a mutable variable from the group
-    pub fn variable_mut<'g>(
-        &'g mut self,
-        name: &str,
-    ) -> error::Result<Option<VariableMut<'g, 'g>>> {
+    pub fn variable_mut<'f>(&'f mut self, name: &str) -> error::Result<Option<VariableMut<'f>>> {
         self.variable(name)
             .map(|var| var.map(|var| VariableMut(var, PhantomData)))
     }
     /// Iterate over all variables in the root group, with mutable access
+    ///
+    /// # Examples
+    /// Use this to get multiple writable variables
+    /// ```no_run
+    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
+    /// let mut file = netcdf::append("file.nc")?;
+    /// let mut vars = file.variables_mut()?.collect::<Result<Vec<_>, _>>()?;
+    /// vars[0].put_value(1_u8, Some(&[2, 5]))?;
+    /// vars[1].put_value(1_u8, Some(&[5, 2]))?;
+    /// # Ok(()) }
+    /// ```
     pub fn variables_mut<'f>(
         &'f mut self,
-    ) -> error::Result<impl Iterator<Item = error::Result<VariableMut<'f, 'f>>>> {
+    ) -> error::Result<impl Iterator<Item = error::Result<VariableMut<'f>>>> {
         self.variables()
             .map(|v| v.map(|var| var.map(|var| VariableMut(var, PhantomData))))
     }
@@ -233,7 +241,7 @@ impl MutableFile {
     }
 
     /// Adds a dimension with the given name and size. A size of zero gives an unlimited dimension
-    pub fn add_dimension<'g>(&'g mut self, name: &str, len: usize) -> error::Result<Dimension<'g>> {
+    pub fn add_dimension<'f>(&'f mut self, name: &str, len: usize) -> error::Result<Dimension<'f>> {
         let _l = LOCK.lock().unwrap();
         super::dimension::add_dimension_at(self.ncid(), name, len)
     }
@@ -256,7 +264,7 @@ impl MutableFile {
         &'f mut self,
         name: &str,
         dims: &[&str],
-    ) -> error::Result<VariableMut<'f, 'f>>
+    ) -> error::Result<VariableMut<'f>>
     where
         T: Numeric,
     {
@@ -264,17 +272,21 @@ impl MutableFile {
         VariableMut::add_from_str(self.ncid(), T::NCTYPE, name, dims)
     }
     /// Adds a variable with a basic type of string
-    pub fn add_string_variable(&mut self, name: &str, dims: &[&str]) -> error::Result<VariableMut> {
+    pub fn add_string_variable<'f>(
+        &'f mut self,
+        name: &str,
+        dims: &[&str],
+    ) -> error::Result<VariableMut<'f>> {
         let _l = LOCK.lock().unwrap();
         VariableMut::add_from_str(self.ncid(), NC_STRING, name, dims)
     }
     /// Adds a variable from a set of unique identifiers, recursing upwards
     /// from the current group if necessary.
-    pub fn add_variable_from_identifiers<T>(
-        &mut self,
+    pub fn add_variable_from_identifiers<'f, T>(
+        &'f mut self,
         name: &str,
         dims: &[dimension::Identifier],
-    ) -> error::Result<VariableMut>
+    ) -> error::Result<VariableMut<'f>>
     where
         T: Numeric,
     {

src/group.rs

@@ -54,13 +54,19 @@ impl<'f> Group<'f> {
     }
 
     /// Get a variable from the group
-    pub fn variable<'g>(&'g self, name: &str) -> error::Result<Option<Variable<'f, 'g>>> {
+    pub fn variable<'g>(&'g self, name: &str) -> error::Result<Option<Variable<'g>>>
+    where
+        'f: 'g,
+    {
         Variable::find_from_name(self.id(), name)
     }
     /// Iterate over all variables in a group
     pub fn variables<'g>(
         &'g self,
-    ) -> error::Result<impl Iterator<Item = error::Result<Variable<'f, 'g>>>> {
+    ) -> error::Result<impl Iterator<Item = error::Result<Variable<'g>>>>
+    where
+        'f: 'g,
+    {
         super::variable::variables_at_ncid(self.id())
     }
 
@@ -70,57 +76,80 @@ impl<'f> Group<'f> {
         Attribute::find_from_name(self.ncid, None, name)
     }
     /// Get all attributes in the group
-    pub fn attributes(&self) -> error::Result<impl Iterator<Item = error::Result<Attribute>>> {
+    pub fn attributes<'a>(
+        &'a self,
+    ) -> error::Result<impl Iterator<Item = error::Result<Attribute<'a>>>> {
         // Need to lock when reading the first attribute (per group)
         let _l = super::LOCK.lock().unwrap();
         crate::attribute::AttributeIterator::new(self.ncid, None)
     }
 
     /// Get a single dimension
-    pub fn dimension(&self, name: &str) -> error::Result<Option<Dimension>> {
+    pub fn dimension<'g>(&'g self, name: &str) -> error::Result<Option<Dimension<'g>>>
+    where
+        'f: 'g,
+    {
         super::dimension::dimension_from_name(self.id(), name)
     }
     /// Iterator over all dimensions
     pub fn dimensions<'g>(
         &'g self,
-    ) -> error::Result<impl Iterator<Item = error::Result<Dimension<'g>>>> {
+    ) -> error::Result<impl Iterator<Item = error::Result<Dimension<'g>>>>
+    where
+        'f: 'g,
+    {
         super::dimension::dimensions_from_location(self.id())
     }
 
     /// Get a group
-    pub fn group(&self, name: &str) -> error::Result<Option<Self>> {
+    pub fn group<'g>(&'g self, name: &str) -> error::Result<Option<Group<'g>>>
+    where
+        'f: 'g,
+    {
         group_from_name(self.id(), name)
     }
     /// Iterator over all subgroups in this group
-    pub fn groups<'g>(&'g self) -> error::Result<impl Iterator<Item = Group<'g>>> {
+    pub fn groups<'g>(&'g self) -> error::Result<impl Iterator<Item = Group<'g>>>
+    where
+        'f: 'g,
+    {
         groups_at_ncid(self.id())
     }
 }
 
 impl<'f> GroupMut<'f> {
     /// Get a mutable variable from the group
-    pub fn variable_mut<'g>(
-        &'g mut self,
-        name: &str,
-    ) -> error::Result<Option<VariableMut<'f, 'g>>> {
+    pub fn variable_mut<'g>(&'g mut self, name: &str) -> error::Result<Option<VariableMut<'g>>>
+    where
+        'f: 'g,
+    {
         self.variable(name)
             .map(|v| v.map(|v| VariableMut(v, PhantomData)))
     }
     /// Iterate over all variables in a group, with mutable access
     pub fn variables_mut<'g>(
         &'g mut self,
-    ) -> error::Result<impl Iterator<Item = error::Result<VariableMut<'f, 'g>>>> {
+    ) -> error::Result<impl Iterator<Item = error::Result<VariableMut<'g>>>>
+    where
+        'f: 'g,
+    {
         self.variables()
             .map(|var| var.map(|var| var.map(|var| VariableMut(var, PhantomData))))
     }
 
     /// Mutable access to subgroup
-    pub fn group_mut(&'f mut self, name: &str) -> error::Result<Option<Self>> {
+    pub fn group_mut<'g>(&'g mut self, name: &str) -> error::Result<Option<GroupMut<'g>>>
+    where
+        'f: 'g,
+    {
         self.group(name)
             .map(|g| g.map(|g| GroupMut(g, PhantomData)))
     }
     /// Iterator over all groups (mutable access)
-    pub fn groups_mut(&'f mut self) -> error::Result<impl Iterator<Item = GroupMut<'f>>> {
+    pub fn groups_mut<'g>(&'g mut self) -> error::Result<impl Iterator<Item = GroupMut<'g>>>
+    where
+        'f: 'g,
+    {
         self.groups().map(|g| g.map(|g| GroupMut(g, PhantomData)))
     }
 
@@ -140,7 +169,7 @@ impl<'f> GroupMut<'f> {
     }
 
     /// Adds a dimension with unbounded size
-    pub fn add_unlimited_dimension(&mut self, name: &str) -> error::Result<Dimension> {
+    pub fn add_unlimited_dimension<'g>(&'g mut self, name: &str) -> error::Result<Dimension<'g>> {
         self.add_dimension(name, 0)
     }
 
@@ -161,7 +190,10 @@ impl<'f> GroupMut<'f> {
     }
 
     /// Add an empty group to the dataset
-    pub fn add_group(&mut self, name: &str) -> error::Result<Self> {
+    pub fn add_group<'g>(&'g mut self, name: &str) -> error::Result<GroupMut<'g>>
+    where
+        'f: 'g,
+    {
         let _l = LOCK.lock().unwrap();
         Self::add_group_at(self.id(), name)
     }
@@ -174,25 +206,30 @@ impl<'f> GroupMut<'f> {
         &'g mut self,
         name: &str,
         dims: &[&str],
-    ) -> error::Result<VariableMut<'f, 'g>>
+    ) -> error::Result<VariableMut<'g>>
     where
         T: Numeric,
+        'f: 'g,
     {
         let _l = LOCK.lock().unwrap();
         VariableMut::add_from_str(self.id(), T::NCTYPE, name, dims)
     }
     /// Adds a variable with a basic type of string
-    pub fn add_string_variable(&mut self, name: &str, dims: &[&str]) -> error::Result<VariableMut> {
+    pub fn add_string_variable<'g>(
+        &mut self,
+        name: &str,
+        dims: &[&str],
+    ) -> error::Result<VariableMut<'g>> {
         let _l = LOCK.lock().unwrap();
         VariableMut::add_from_str(self.id(), NC_STRING, name, dims)
     }
     /// Adds a variable from a set of unique identifiers, recursing upwards
     /// from the current group if necessary.
-    pub fn add_variable_from_identifiers<T>(
-        &mut self,
+    pub fn add_variable_from_identifiers<'g, T>(
+        &'g mut self,
         name: &str,
         dims: &[super::dimension::Identifier],
-    ) -> error::Result<VariableMut>
+    ) -> error::Result<VariableMut<'g>>
     where
         T: Numeric,
     {

src/variable.rs

@@ -16,9 +16,9 @@ use std::marker::Sized;
 #[allow(clippy::doc_markdown)]
 /// This struct defines a netCDF variable.
 #[derive(Debug, Clone)]
-pub struct Variable<'f, 'g> {
+pub struct Variable<'g> {
     /// The variable name
-    pub(crate) dimensions: Vec<Dimension<'f>>,
+    pub(crate) dimensions: Vec<Dimension<'g>>,
     /// the netcdf variable type identifier (from netcdf-sys)
     pub(crate) vartype: nc_type,
     pub(crate) ncid: nc_type,
@@ -27,14 +27,14 @@ pub struct Variable<'f, 'g> {
 }
 
 #[derive(Debug)]
-/// Mutable access to a variable
-pub struct VariableMut<'f, 'g>(
-    pub(crate) Variable<'f, 'g>,
+/// Mutable access to a variable.
+pub struct VariableMut<'g>(
+    pub(crate) Variable<'g>,
     pub(crate) PhantomData<&'g mut nc_type>,
 );
 
-impl<'f, 'g> std::ops::Deref for VariableMut<'f, 'g> {
-    type Target = Variable<'f, 'g>;
+impl<'g> std::ops::Deref for VariableMut<'g> {
+    type Target = Variable<'g>;
     fn deref(&self) -> &Self::Target {
         &self.0
     }
@@ -52,11 +52,8 @@ pub enum Endianness {
 }
 
 #[allow(clippy::len_without_is_empty)]
-impl<'f, 'g> Variable<'f, 'g> {
-    pub(crate) fn find_from_name(
-        ncid: nc_type,
-        name: &str,
-    ) -> error::Result<Option<Variable<'f, 'g>>> {
+impl<'g> Variable<'g> {
+    pub(crate) fn find_from_name(ncid: nc_type, name: &str) -> error::Result<Option<Variable<'g>>> {
         let cname = super::utils::short_name_to_bytes(name)?;
         let mut varid = 0;
         let e = unsafe { nc_inq_varid(ncid, cname.as_ptr() as *const _, &mut varid) };
@@ -151,7 +148,7 @@ impl<'f, 'g> Variable<'f, 'g> {
         }
     }
 }
-impl<'f, 'g> VariableMut<'f, 'g> {
+impl<'g> VariableMut<'g> {
     /// Sets compression on the variable. Must be set before filling in data.
     ///
     /// `deflate_level` can take a value 0..=9, with 0 being no
@@ -200,7 +197,7 @@ impl<'f, 'g> VariableMut<'f, 'g> {
     }
 }
 
-impl<'f, 'g> Variable<'f, 'g> {
+impl<'g> Variable<'g> {
     /// Checks for array mismatch
     fn check_indices(&self, indices: &[usize], putting: bool) -> error::Result<()> {
         if indices.len() != self.dimensions.len() {
@@ -684,7 +681,7 @@ impl std::ops::Deref for NcString {
     }
 }
 
-impl<'f, 'g> VariableMut<'f, 'g> {
+impl<'g> VariableMut<'g> {
     /// Adds an attribute to the variable
     pub fn add_attribute<T>(&mut self, name: &str, val: T) -> error::Result<Attribute>
     where
@@ -695,7 +692,7 @@ impl<'f, 'g> VariableMut<'f, 'g> {
     }
 }
 
-impl<'f, 'g> Variable<'f, 'g> {
+impl<'g> Variable<'g> {
     ///  Fetches one specific value at specific indices
     ///  indices must has the same length as self.dimensions.
     pub fn value<T: Numeric>(&self, indices: Option<&[usize]>) -> error::Result<T> {
@@ -900,7 +897,7 @@ impl<'f, 'g> Variable<'f, 'g> {
     }
 }
 
-impl<'f, 'g> VariableMut<'f, 'g> {
+impl<'g> VariableMut<'g> {
     /// Put a single value at `indices`
     pub fn put_value<T: Numeric>(
         &mut self,
@@ -1098,7 +1095,7 @@ impl<'f, 'g> VariableMut<'f, 'g> {
     }
 }
 
-impl<'f, 'g> VariableMut<'f, 'g> {
+impl<'g> VariableMut<'g> {
     pub(crate) fn add_from_str(
         ncid: nc_type,
         xtype: nc_type,
@@ -1141,12 +1138,9 @@ impl<'f, 'g> VariableMut<'f, 'g> {
     }
 }
 
-pub(crate) fn variables_at_ncid<'f, 'g>(
+pub(crate) fn variables_at_ncid<'g>(
     ncid: nc_type,
-) -> error::Result<impl Iterator<Item = error::Result<Variable<'f, 'g>>>>
-where
-    'f: 'g,
-{
+) -> error::Result<impl Iterator<Item = error::Result<Variable<'g>>>> {
     let mut nvars = 0;
     unsafe {
         error::checked(nc_inq_varids(ncid, &mut nvars, std::ptr::null_mut()))?;
@@ -1176,12 +1170,12 @@ where
     }))
 }
 
-pub(crate) fn add_variable_from_identifiers<'f, 'g>(
+pub(crate) fn add_variable_from_identifiers<'g>(
     ncid: nc_type,
     name: &str,
     dims: &[super::dimension::Identifier],
     xtype: nc_type,
-) -> error::Result<VariableMut<'f, 'g>> {
+) -> error::Result<VariableMut<'g>> {
     let cname = super::utils::short_name_to_bytes(name)?;
 
     let dimensions = dims

tests/lib.rs

@@ -1292,14 +1292,12 @@ fn dimension_identifiers() {
         let g = &mut file.add_group("g").unwrap();
         let dim = &g.add_dimension("x", 5).unwrap();
         let vgid = dim.identifier();
-        let mut gg = file
-            .group_mut("g")
-            .unwrap()
-            .unwrap()
-            .add_group("g")
-            .unwrap();
-        let dim = &gg.add_dimension("x", 7).unwrap();
-        let vggid = dim.identifier();
+        let vggid = {
+            let mut g = file.group_mut("g").unwrap().unwrap();
+            let mut gg = g.add_group("g").unwrap();
+            let dim = &gg.add_dimension("x", 7).unwrap();
+            dim.identifier()
+        };
 
         // Create variables
         file.add_variable_from_identifiers::<i8>("v_self_id", &[vrootid])