multiboot2: simplify usage of cast_tag::<T>()

multiboot2/src/lib.rs

@@ -218,14 +218,13 @@ impl BootInformation {
 
     /// Search for the ELF Sections tag.
     pub fn elf_sections_tag(&self) -> Option<ElfSectionsTag> {
-        self.get_tag(TagType::ElfSections)
+        self.get_tag::<Tag, _>(TagType::ElfSections)
             .map(|tag| unsafe { elf_sections::elf_sections_tag(tag, self.offset) })
     }
 
     /// Search for the Memory map tag.
     pub fn memory_map_tag(&self) -> Option<&MemoryMapTag> {
-        self.get_tag(TagType::Mmap)
-            .map(|tag| tag.cast_tag::<MemoryMapTag>())
+        self.get_tag::<MemoryMapTag, _>(TagType::Mmap)
     }
 
     /// Get an iterator of all module tags.
@@ -235,45 +234,39 @@ impl BootInformation {
 
     /// Search for the BootLoader name tag.
     pub fn boot_loader_name_tag(&self) -> Option<&BootLoaderNameTag> {
-        self.get_tag(TagType::BootLoaderName)
-            .map(|tag| tag.cast_tag::<BootLoaderNameTag>())
+        self.get_tag::<BootLoaderNameTag, _>(TagType::BootLoaderName)
     }
 
     /// Search for the Command line tag.
     pub fn command_line_tag(&self) -> Option<&CommandLineTag> {
-        self.get_tag(TagType::Cmdline)
-            .map(|tag| tag.cast_tag::<CommandLineTag>())
+        self.get_tag::<CommandLineTag, _>(TagType::Cmdline)
     }
 
     /// Search for the VBE framebuffer tag. The result is `Some(Err(e))`, if the
     /// framebuffer type is unknown, while the framebuffer tag is present.
     pub fn framebuffer_tag(&self) -> Option<Result<FramebufferTag, UnknownFramebufferType>> {
-        self.get_tag(TagType::Framebuffer)
+        self.get_tag::<Tag, _>(TagType::Framebuffer)
             .map(framebuffer::framebuffer_tag)
     }
 
     /// Search for the EFI 32-bit SDT tag.
     pub fn efi_sdt_32_tag(&self) -> Option<&EFISdt32> {
-        self.get_tag(TagType::Efi32)
-            .map(|tag| tag.cast_tag::<EFISdt32>())
+        self.get_tag::<EFISdt32, _>(TagType::Efi32)
     }
 
     /// Search for the EFI 64-bit SDT tag.
     pub fn efi_sdt_64_tag(&self) -> Option<&EFISdt64> {
-        self.get_tag(TagType::Efi64)
-            .map(|tag| tag.cast_tag::<EFISdt64>())
+        self.get_tag::<EFISdt64, _>(TagType::Efi64)
     }
 
     /// Search for the (ACPI 1.0) RSDP tag.
     pub fn rsdp_v1_tag(&self) -> Option<&RsdpV1Tag> {
-        self.get_tag(TagType::AcpiV1)
-            .map(|tag| tag.cast_tag::<RsdpV1Tag>())
+        self.get_tag::<RsdpV1Tag, _>(TagType::AcpiV1)
     }
 
     /// Search for the (ACPI 2.0 or later) RSDP tag.
     pub fn rsdp_v2_tag(&self) -> Option<&RsdpV2Tag> {
-        self.get_tag(TagType::AcpiV2)
-            .map(|tag| tag.cast_tag::<RsdpV2Tag>())
+        self.get_tag::<RsdpV2Tag, _>(TagType::AcpiV2)
     }
 
     /// Search for the EFI Memory map tag, if the boot services were exited.
@@ -283,36 +276,30 @@ impl BootInformation {
     pub fn efi_memory_map_tag(&self) -> Option<&EFIMemoryMapTag> {
         // If the EFIBootServicesNotExited is present, then we should not use
         // the memory map, as it could still be in use.
-        match self.get_tag(TagType::EfiBs) {
+        match self.get_tag::<Tag, _>(TagType::EfiBs) {
             Some(_tag) => None,
-            None => self
-                .get_tag(TagType::EfiMmap)
-                .map(|tag| tag.cast_tag::<EFIMemoryMapTag>()),
+            None => self.get_tag::<EFIMemoryMapTag, _>(TagType::EfiMmap),
         }
     }
 
     /// Search for the EFI 32-bit image handle pointer.
     pub fn efi_32_ih(&self) -> Option<&EFIImageHandle32> {
-        self.get_tag(TagType::Efi32Ih)
-            .map(|tag| tag.cast_tag::<EFIImageHandle32>())
+        self.get_tag::<EFIImageHandle32, _>(TagType::Efi32Ih)
     }
 
     /// Search for the EFI 64-bit image handle pointer.
     pub fn efi_64_ih(&self) -> Option<&EFIImageHandle64> {
-        self.get_tag(TagType::Efi64Ih)
-            .map(|tag| tag.cast_tag::<EFIImageHandle64>())
+        self.get_tag::<EFIImageHandle64, _>(TagType::Efi64Ih)
     }
 
     /// Search for the Image Load Base Physical Address.
     pub fn load_base_addr(&self) -> Option<&ImageLoadPhysAddr> {
-        self.get_tag(TagType::LoadBaseAddr)
-            .map(|tag| tag.cast_tag::<ImageLoadPhysAddr>())
+        self.get_tag::<ImageLoadPhysAddr, _>(TagType::LoadBaseAddr)
     }
 
     /// Search for the VBE information tag.
     pub fn vbe_info_tag(&self) -> Option<&VBEInfoTag> {
-        self.get_tag(TagType::Vbe)
-            .map(|tag| tag.cast_tag::<VBEInfoTag>())
+        self.get_tag::<VBEInfoTag, _>(TagType::Vbe)
     }
 
     fn get(&self) -> &BootInformationInner {
@@ -336,7 +323,8 @@ impl BootInformation {
     /// the MBI. Custom tags must be `Sized`. Hence, they are not allowed to contain a field such
     /// as `name: [u8]`.
     ///
-    /// ```rust
+    /// **Belows example needs Rust 1.64 or newer because of std::ffi imports!**
+    /// ```ignore
     /// use std::ffi::{c_char, CStr};
     /// use multiboot2::TagTypeId;
     ///
@@ -349,18 +337,21 @@ impl BootInformation {
     ///     name: u8,
     /// }
     ///
-    /// let tag = bi
-    ///     .get_tag(0x1337)
-    ///     .unwrap()
+    /// let mbi = unsafe { multiboot2::load(0xdeadbeef).unwrap() };
+    ///
+    /// let tag = mbi
     ///     // type definition from end user; must be `Sized`!
-    ///     .cast_tag::<CustomTag>();
+    ///     .get_tag::<CustomTag, _>(0x1337)
+    ///     .unwrap();
     /// let name = &tag.name as *const u8 as *const c_char;
     /// let str = unsafe { CStr::from_ptr(name).to_str().unwrap() };
     /// assert_eq!(str, "name");
     /// ```
-    pub fn get_tag(&self, typ: impl Into<TagTypeId>) -> Option<&Tag> {
+    pub fn get_tag<Tag, TagType: Into<TagTypeId>>(&self, typ: TagType) -> Option<&Tag> {
         let typ = typ.into();
-        self.tags().find(|tag| tag.typ == typ)
+        self.tags()
+            .find(|tag| tag.typ == typ)
+            .map(|tag| tag.cast_tag::<Tag>())
     }
 
     fn tags(&self) -> TagIter {
@@ -1499,6 +1490,7 @@ mod tests {
         consumer(MbiLoadError::IllegalAddress)
     }
 
+    #[test]
     fn custom_tag() {
         const CUSTOM_TAG_ID: u32 = 0x1337;
 
@@ -1553,7 +1545,7 @@ mod tests {
             name: u8,
         }
 
-        let tag = bi.get_tag(CUSTOM_TAG_ID).unwrap().cast_tag::<CustomTag>();
+        let tag = bi.get_tag::<CustomTag, _>(CUSTOM_TAG_ID).unwrap();
 
         // strlen without null byte
         let strlen = tag.size as usize - mem::size_of::<CommandLineTag>();
@@ -1606,10 +1598,10 @@ mod tests {
         let bi = unsafe { load(addr) };
         let bi = bi.unwrap();
 
-        let _tag = bi.get_tag(TagType::Cmdline).unwrap();
+        let _tag = bi.get_tag::<CommandLineTag, _>(TagType::Cmdline).unwrap();
 
-        let _tag = bi.get_tag(1).unwrap();
+        let _tag = bi.get_tag::<CommandLineTag, _>(1).unwrap();
 
-        let _tag = bi.get_tag(TagTypeId::new(1)).unwrap();
+        let _tag = bi.get_tag::<CommandLineTag, _>(TagTypeId::new(1)).unwrap();
     }
 }